Phone the U.S. Department of State at 1-877-487-2778. If you are in the United States, report your lost passport to the state department Monday through Friday from the eastern standard hours of 8 a.m. to 10 p.m.
Visit the U.S. Consulate or Embassy office if you are outside the United States. If you are unsure where to go, ask a local police officer or visit a local travel agent's office, or look up the nearest consulate by visiting www.http://travel.state.gov/passport/passport_1738.html
Send the U.S. State Department a completed DS-64 form. Download a copy of the "Statement Regarding a Lost or Stolen Passport" and mail it to: U.S. Department of State, Passport Service, Consular Lost/Stolen Passport Section, 1111 19th Street, NW, Suite 500, Washington, DC 20036.