UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 13D

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 3)*

(Name of Issuer)

(Title of Class of Securities)

(CUSIP Number)

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

(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 that is the subject of this Schedule 13D, and is filing this schedule because of §§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 §240.13d-7 for other parties to whom copies are to be sent.

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).

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This Amendment No. 3 (this “Amendment No. 3”) relates to, amends and supplements where indicated the Statement on Schedule 13D originally filed with the Securities and Exchange Commission on December 19, 2011 (the “Original Statement”), as amended by the Statement on Schedule 13D/A as filed with the Securities and Exchange Commission on December 20, 2011 (“Amendment No. 1”) and the Statement on Schedule 13D/A as filed with the Securities and Exchange Commission on July 12, 2012 (“Amendment No. 2”), by and on behalf of Lacuna Hedge Fund LLLP (“Lacuna Hedge”), Lacuna Hedge GP LLLP and Lacuna, LLC (collectively, with Lacuna Hedge and Lacuna Hedge GP LLLP, the “Lacuna Entities”) and relates to the common stock, $0.001 par value per share (“Common Stock”), of Rainmaker Systems, Inc., a Delaware corporation (the “Issuer”). This Amendment No. 3, Amendment No. 2, Amendment No. 1 and the Original Statement are collectively referred to herein as the “Schedule 13D.”

Capitalized terms used herein but not defined herein shall have the meanings ascribed to them in the Original Statement. This Amendment No. 3 amends and supplements the Original Statement, Amendment No. 2 and Amendment No. 1 as specifically set forth herein. Except as set forth below, all previous Items in the Original Statement, as amended by Amendment No. 2 and Amendment No. 1, remain unchanged.

This Amendment No. 3 is being filed to amend Item 4 as set forth below and to update the number of shares of Common Stock beneficially held by the Lacuna Entities as a result of the transactions described below.

Item 4. Purpose of Transaction

Item 4 of the Schedule 13D is hereby supplemented by adding the following paragraph:

On March 1, 2012, Lacuna Hedge purchased an aggregate of 1,000 shares of Common Stock of the Issuer in open market transactions. On March 2, 2012, Lacuna Hedge sold 6,467 shares of Common Stock of the Issuer in an open market transaction. Those transactions were not disclosed in Amendment No. 2. Between July 16, 2012 and August 10, 2012, Lacuna Hedge sold an aggregate of 1,737,357 shares of Common Stock of the Issuer in open market transactions.

Item 5. Interest in Securities of the Issuer

Item 5 of the Schedule 13D is hereby amended and supplemented with the following:

(a) and (b) As of August 15, 2012, none of the Lacuna Entities and none of the Listed Persons beneficially owned any Common Stock of the Issuer.

The information provided and incorporated by reference in Items 2, 3 and 4 is hereby incorporated by reference.

(c)

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All of the above transactions were executed through a broker and settled through facilities of The Depository Trust & Clearing Corporation.

(d) Not Applicable.

(e) The Lacuna Entities ceased to be the beneficial owner of more than five percent of the Common Stock of the Issuer on July 19, 2012.

Item 7. Material to Be Filed as Exhibits

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SIGNATURE

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.

EXECUTED this 15^th day of August, 2012.

The original statement shall be signed by each person on whose behalf the statement is filed or his authorized representative. If the statement is signed on behalf of a person by his authorized representative (other than an executive officer or general partner of the filing person), evidence of the representative’s authority to sign on behalf of such person shall be filed with the statement: provided, however, that a power of attorney for this purpose which is already on file with the Commission may be incorporated by reference. The name and any title of each person who signs the statement shall be typed or printed beneath his signature.

Attention: Intentional misstatements or omissions of fact

constitute Federal criminal violations (See 18 U.S.C. 1001)

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EXHIBIT INDEX

Exhibit A

JOINT FILING AGREEMENT

Pursuant to Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, as amended, the undersigned hereby agree that the attached Schedule 13D is being filed on behalf of each of the undersigned.

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.

EXECUTED this 15^th day of August, 2012.