UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

(Rule 13d-101)

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT

TO § 240.13D-1(A) AND AMENDMENTS THERETO FILED

PURSUANT TO § 240.13D-2(A)

(Amendment No. 8)

Tangoe, Inc.

(Name of Issuer)

Common Stock, $0.0001 par value

(Title of Class of Securities)

87582Y108

(CUSIP Number)

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

January 2, 2017

(Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition which is the subject of this Schedule 13D, and is filing this schedule because of Sections 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.  ☐

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Section 240.13d-7 for other parties to whom copies are to be sent.

The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

This Amendment No. 8 to Schedule 13D is being filed by Clearlake Capital Partners IV Finance, L.P., Clearlake Capital Partners IV GP, L.P., Clearlake Capital Partners, LLC, CCG Operations, LLC (such entities together, the “Clearlake Entities”), Behdad Eghbali and José E. Feliciano (the Clearlake Entities together with Messrs. Eghbali and Feliciano, the “Reporting Persons”), pursuant to §240.13d-2(a), to amend the Schedule 13D filed by the Reporting Persons on November 30, 2015 (the “Initial Schedule 13D”), as amended by Amendment No. 1 thereto filed by the Reporting Persons on December 15, 2015, by Amendment No. 2 thereto filed by the Reporting Persons on January 11, 2016, by Amendment No. 3 thereto filed by the Reporting Persons on January 20, 2016, by Amendment No. 4 thereto filed by the Reporting Persons on March 22, 2016, by Amendment No. 5 thereto filed by the Reporting Persons on April 14, 2016, by Amendment No. 6 thereto filed by the Reporting Persons on June 24, 2016, and by Amendment No. 7 thereto filed by the Reporting Persons on September 9, 2016 (the Initial Schedule 13D together with such amendments, the “Schedule 13D”), relating to the Common Stock, $0.0001 par value per share, of Tangoe, Inc. Except as set forth below, all Items of the Schedule 13D remain unchanged. All capitalized terms not otherwise defined herein shall have the meanings ascribed to such terms in the Schedule 13D.

Item 1 of the Schedule 13D is hereby amended by the addition of the following:

Vector Capital IV, L.P., Vector Capital Partners IV, L.P., Vector Entrepreneur Fund III, L.P., Vector Capital Partners III, L.P., Vector Capital, L.L.C. and Alexander R. Slusky (collectively, the “Vector Entities”) are jointly filing a separate amendment to such parties’ existing Schedule 13D on the date hereof (the “Vector 13D”) reporting beneficial ownership of shares of common stock, par value $0.0001 per share, of the Company (“Company Shares”). The Reporting Persons may be deemed members of a “group” (within the meaning of Rule 13d-5 under the Act) with the Vector Entities.

Item 4 of the Schedule 13D is hereby amended by the addition of the following:

On January 2, 2017, Clearlake Capital Group, L.P. (an affiliate of the Clearlake Entities) and Vector Capital Management, L.P. (an affiliate of the Vector Entities) submitted a non-binding indication of interest (the “IOI”) to the Company pursuant to which the Clearlake Entities and the Vector Entities proposed to acquire all of the issued and outstanding Company Shares, other than the Company Shares held by the Reporting Persons and the Vector Entities, for $7.00 per share. A copy of the IOI is filed herewith as an exhibit and incorporated herein by reference, and any descriptions herein of the IOI are qualified in their entirety by reference to the IOI filed herewith.

Item 5(a) of the Schedule 13D is hereby amended by the addition of the following:

vii. The disclosure in this Amendment No. 8 assumes that the Vector Entities own, in aggregate, 3,964,051 Company Shares, which is the number of Company Shares the Vector Entities disclosed they owned, in aggregate, in the Vector 13D. The Reporting Persons may be deemed members of a “group” (within the meaning of Rule 13d-5 under the Act) with the Vector Entities, and as a result each of the Reporting Persons may have shared voting power over the Company Shares owned by the Vector Entities.

Item 7 is hereby amended to add the following exhibit:

SIGNATURES

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: January 3, 2017

Exhibit 3

PRIVILEGED AND CONFIDENTIAL

NON-BINDING, PRELIMINARY INDICATION OF INTEREST

RELATING TO THE POTENTIAL ACQUISITION OF

Tangoe, Inc. (“Tangoe” or the “Company”)

January 2, 2017

This non-binding, indication of interest (the “Indication”) relates to the potential acquisition of the Company (the “Transaction”) by Clearlake Capital Group, L.P. (“Clearlake”) and Vector Capital Management, L.P. (“Vector”) and their respective affiliates (together, the “Purchase Group”) and is provided in response to a specific written invitation from the Company pursuant to the terms of the respective confidentiality agreements entered into on September 8, 2016 by each of Clearlake and Vector, on the one hand, and the Company, on the other hand. This Indication is for discussion purposes only and does not impose any obligation on any party relating to a Transaction. Notwithstanding anything to the contrary below or in any other prior or future oral or written communications between the parties, no such obligation will arise unless and until the execution of definitive Transaction documentation (the “Definitive Agreement”).

First, we very much appreciate the Board’s willingness to receive our Indication – and moreover, appreciate the time, effort and resources the management team has invested in exploring a potential strategic alternative involving our respective firms – independently initially, and more recently permitting our firms to consider submitting a joint proposal in order to permit a Transaction on terms that maximize value to stockholders under the circumstances. Second, we appreciate the complex, time-intensive matters that the Board and the current leadership group have been grappling with. We recognize the Board and the current team’s concerted efforts and genuine motivations to enhance long-term value for employees, customers and stockholders. Finally, we have observed the major issues the Company and team are facing, much of which will take significant time, cost and effort to address. As two of the Company’s largest stockholders, we believe it is critical for the Company to pursue a strategic alternative imminently, and it is with that mutual objective that we are hereby joining efforts in order to put forth the Indication below to help address Tangoe’s current challenging situation.

About Clearlake

Clearlake is a private investment firm with a sector-focused approach. The firm seeks to partner with world-class management teams by providing patient, long-term capital to dynamic businesses that can benefit from Clearlake’s operational and strategic expertise. The firm’s core target sectors include software and technology enabled business services, communications, industrials, and energy services. Clearlake currently has over $3 billion of assets under management. Clearlake has a strong track record of sponsoring leading technology and tech-enabled services companies. Clearlake is a principal stockholder of Tangoe with nearly a 15% stake.

About Vector

Vector is a leading private equity firm specializing in buyouts, spinouts, and recapitalizations of established technology businesses. With over $3 billion in capital under management, Vector identifies and pursues investments in both private and public markets. Vector is a patient capital provider and actively partners with management teams to devise and execute new financial and business strategies that materially transform the fundamental standing of businesses. Along with a nearly 20 year track record of leading investments in the software and broader technology sector, Vector has also completed a number of transactions involving public company targets with accounting restatements and regulatory matters, including similar situations involving unaudited financial statements. Vector is a principal stockholder of Tangoe with an approximately 10% stake.

Purchase Group Proposal

The Purchase Group together would beneficially own approximately 25% of the Company’s outstanding capital stock, and represent the largest stockholder group of the Company. Our firms had independent but similar goals in becoming significant stockholders of the Company – namely to leverage our respective investment experiences in turnaround situations to help craft a strategy for the Company to address its various challenges and maximize value for all of its stockholders. In conjunction with separately signing confidentiality agreements nearly four months ago with our firms, each of Clearlake and Vector have invested extensive resources and conducted significant due diligence on the Company. During this time, we have observed several critical issues facing the Company, among which include a comprehensive accounting restatement, the failure to make any significant product development announcements, significant management turnover, and the inability to provide audited financial information (or a comprehensive business update) since November 2015. From our prior investment experience, we are acutely aware how long and arduous addressing these challenges will be and the difficulties presented for any management team to try and attempt these activities under the scrutiny of public markets. It should also be noted that during this time, other than a preliminary non-binding indication of interest disclosed by another Company stockholder in a filing last Thursday, December 29, 2016, no other strategic alternatives have been presented for the benefit of stockholders.

We strongly believe the time has come for Tangoe to move swiftly towards a transaction that enables the Company to undergo the required operational and financial transformation that can only happen as a private company. We believe the Indication represents a highly attractive, detailed and actionable alternative that we are prepared to move forward on expeditiously. We would also add that – while we believe our Indication represents the best opportunity to maximize stockholder value – as large public stockholders, we are very supportive of the Company seeking other available alternatives that might also maximize stockholder value. Regardless of the ultimate outcome, it is our strong belief that in order to preserve and maximize the long-term value of the business, the Company needs to move quickly towards a transaction before the Company is faced with further impairment of value and available options.

2

The following outline describes the key terms of our Indication:

Non-Binding Indication of Interest

3

We believe this proposal reflects immediate and compelling value for the Company, its stockholders and employees. We hold the Company and its current management team in the highest regard and commend them for their admirable efforts under very challenging circumstances. However, we believe the Company must act now to choose a strategic alternative that addresses the concerns of all constituencies involved and helps put Tangoe on a path back to stability as soon as possible.

As our legal advisors have discussed in the context of the Company’s invitation to submit this Indication, each of Vector and Clearlake will be filing this letter as an exhibit to an amendment to its Schedule 13D with respect to the Company.

4

Please do not hesitate to contact the respective Vector or Clearlake teams with any questions regarding this letter.

Thank you,

5