SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K/A

(Amendment No. One)

(Mark One)

For the fiscal year ended December 31, 2011

or

For the transition period from              to             

Commission file number 000-49806

FIRST PACTRUST BANCORP, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (949) 236-5211

Securities Registered Pursuant to Section 12(b) of the Act:

Common Stock, par value $0.01 per share

(Title of class)

Nasdaq Global Market

(Name of each exchange on which registered)

Securities Registered Pursuant to Section 12(g) of the Act:

None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    YES  ¨.    NO  x.

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.    YES  ¨.    NO  x.

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports) and (2) has been subject to such filing requirements for the past 90 days.    YES  x.    NO  ¨.

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this Chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    YES  x    NO  ¨.

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer,” “and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act).    ¨  YES.    x  NO.

The aggregate market value of the voting stock held by non-affiliates of the registrant, computed by reference to the closing price of such stock on the Nasdaq Global Market as of June 30, 2011, was $142.4 million. (The exclusion from such amount of the market value of the shares owned by any person shall not be deemed an admission by the registrant that such person is an affiliate of the registrant.) As of March 15, 2012, there were issued and outstanding 11,660,444 shares of the Registrant’s Common Stock.

DOCUMENTS INCORPORATED BY REFERENCE

PART III of Form 10-K—Portions of the Proxy Statement for the Annual Meeting of Shareholders to be held during May 2012.

EXPLANATORY NOTE

The sole purpose of this amendment on Form 10-K/A to the Annual Report on Form 10-K of First PacTrust Bancorp, Inc. (the “Company”) for the year ended December 31, 2011 is to add Exhibit 21, Subsidiaries of the Registrant, to the list of exhibits in Item 15 of the Form 10-K, to make other minor changes to such list of exhibits, to file Exhibit 21 to the Form 10-K and to check the box on the Form 10-K cover page to indicate the Company’s smaller reporting company status with respect to the Form 10-K (which box was inadvertently left unchecked on the cover page of the original Form 10-K). Aside from the inclusion with this amendment of new certifications required by Rules 13a-14(a) and 13a-14(b) under the Securities Exchange Act of 1934, as amended, no other change is being made to the original Form 10-K.

Item 15. Exhibits and Financial Statement Schedules

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2

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4

SIGNATURE

Pursuant to the requirements of Section 13 or 15 (d) of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

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