Lost Persons Looking for someone? The U.S. Social Security Administration will attempt to forward letters to persons whose address is unknown. One may send an UNSEALED letter with a covering letter which explains the relationship of the writer with the addressee and the reason you want the letter forwarded. Include the person's name, Social Security Number, birthplace, birthdate and name of parents, if known. Mail to: Social Security Administration Letter Forwarding Unit 6401 Security Blvd. Baltimore, MD 21235