Locate the paperwork that came with your passport when you first obtained it. Your nine-digit passport number will be located near the top of the first page of this paperwork. You were also issued a wallet-sized card that has your passport number with this paperwork -- try to locate this card if you can't find the paperwork.
Contact the family and friends you gave photocopies of your passport to. It's recommended that you make photocopies before traveling anywhere.
Contact a travel agent or hotel representative who used your passport number to make a booking. These individuals could still have your passport number in their records.
Write a notarized letter to Passport Services, a division of the United States Bureau of Consular Affairs, to obtain a copy of your passport record. The fee for obtaining this record is $50. Include in your letter your full name at birth, any name changes, your date and place of birth, your mailing address, your telephone number, your e-mail address, your reason for requesting the record, the date your passport was issued and a copy of a valid federal- or state-issued photo identification.
