Go to the U.S. Department of State's International Travel website at travel.state.gov. Click on "Passport" at the top of the screen. Click on "Lost or Stolen Passport" on the left side of the next screen. Click on "Form DS-64: Statement Regarding a Lost or Stolen Passport" near the middle of the screen.
Print the Statement Regarding a Lost or Stolen Passport, by clicking on "Print a Blank Form DS-64" near the middle of the page. The form will open as a PDF file. You can fill the form out online and then print it.
Sign and date the form and submit it to:
U.S. Department of State
Passport Services
Consular Lost/Stolen Passport Section
1111 19th Street, NW, Suite 500
Washington, DC 20036