13G Filing: Soros Fund Management and Servicesource International Inc. (SREV)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No.    )*

SERVICESOURCE
INTERNATIONAL, INC.

(Name of Issuer)

Common Stock, $0.0001 par value

(Title of Class of Securities)

81763U100

(CUSIP Number)

December 3, 2017

(Date of Event which Requires Filing of this Statement)

Check the appropriate box to
designate the rule pursuant to which this Schedule is filed:

☐ Rule 13d-1(b)

☒ Rule 13d-1(c)

☐
Rule 13d-1(d)

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).

SIGNATURES

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

EXHIBIT INDEX

EXHIBIT A

JOINT FILING AGREEMENT

The undersigned hereby agree that the Schedule 13G with respect to the Common Stock, $0.0001 par value, of ServiceSource International, Inc.,
dated as of January 3, 2018, is, and any amendments thereto (including amendments on Schedule 13D) signed by each of the undersigned shall be, filed on behalf of each of us pursuant to and in accordance with the provisions of Rule 13d-1(k) under the Securities Exchange Act of 1934.

EXHIBIT B

POWER OF ATTORNEY

KNOW
ALL MEN BY THESE PRESENT, that I, GEORGE SOROS, hereby make, constitute and appoint each of MARYANN CANFIELD, JODYE ANZALOTTA, JAY SCHOENFARBER, THOMAS OGRADY, REGAN ONEILL and ROBERT SOROS, acting individually, as my agent and attorney-in-fact for the purpose of executing in my name, (a) in my personal capacity or (b) in my capacity as Chairman of, member of or in other capacities with
Soros Fund Management LLC (SFM LLC) and each of its affiliates or entities advised by me or SFM LLC, all documents, certificates, instruments, statements, filings and agreements (documents) to be filed with or delivered to
any foreign or domestic governmental or regulatory body or required or requested by any other person or entity pursuant to any legal or regulatory requirement relating to the acquisition, ownership, management or disposition of securities, futures
contracts or other investments, and any other documents relating or ancillary thereto, including without limitation all documents relating to filings with the Commodities Futures Trading Commission and National Futures Association, the United States
Securities and Exchange Commission (the SEC) pursuant to the Securities Act of 1933 or the Securities Exchange Act of 1934 (the Act) and the rules and regulations promulgated thereunder, including all documents relating to
the beneficial ownership of securities required to be filed with the SEC pursuant to Section 13(d) or Section 16(a) of the Act and any information statements on Form 13F required to be filed with the SEC pursuant to Section 13(f) of
the Act.

All past acts of these attorneys-in-fact in
furtherance of the foregoing are hereby ratified and confirmed.

Execution of this power of attorney revokes that certain Power of
Attorney dated as of the 26th day of June, 2009 with respect to the same matters addressed above.

This power of attorney shall be valid
from the date hereof until revoked by me.

IN WITNESS WHEREOF, I have executed this instrument as of the 24th day of November, 2015.

EXHIBIT C

POWER OF ATTORNEY

KNOW
ALL MEN BY THESE PRESENT, that I, ROBERT SOROS, hereby make, constitute and appoint each of MARYANN CANFIELD, JODYE ANZALOTTA, JAY SCHOENFARBER, THOMAS OGRADY and REGAN ONEILL, acting individually, as my agent and attorney-in-fact for the purpose of executing in my name, (a) in my personal capacity or (b) in my capacity as Deputy Chairman of, member of or in other capacities
with Soros Fund Management LLC (SFM LLC) and each of its affiliates or entities advised by me or SFM LLC, all documents, certificates, instruments, statements, filings and agreements (documents) to be filed with or delivered
to any foreign or domestic governmental or regulatory body or required or requested by any other person or entity pursuant to any legal or regulatory requirement relating to the acquisition, ownership, management or disposition of securities,
futures contracts or other investments, and any other documents relating or ancillary thereto, including without limitation all documents relating to filings with the Commodities Futures Trading Commission and National Futures Association, the
United States Securities and Exchange Commission (the SEC) pursuant to the Securities Act of 1933 or the Securities Exchange Act of 1934 (the Act) and the rules and regulations promulgated thereunder, including all documents
relating to the beneficial ownership of securities required to be filed with the SEC pursuant to Section 13(d) or Section 16(a) of the Act and any information statements on Form 13F required to be filed with the SEC pursuant to
Section 13(f) of the Act.

All past acts of these
attorneys-in-fact in furtherance of the foregoing are hereby ratified and confirmed.

Execution of this power of attorney revokes that certain Power of Attorney dated as of the 3rd day of October, 2007 with respect to the same
matters addressed above.

This power of attorney shall be valid from the date hereof until revoked by me.

IN WITNESS WHEREOF, I have executed this instrument as of the 30th day of November, 2015.