The United States Postal Service offers ways for people to find out a forwarding address of friends and family members. A friend who has moved and did not leave their new address does not have to be difficult to find. Write a letter and place your return address information on it so that the post office will know where to send the information that you have request. Without your mailing address on the letter you will not be able to find out the information that you need to know.
Write a letter and send it to the person's last known mailing address. When you go to the post office to mail the letter request that "Address Correction Requested" be placed on your letter. This allows the post office to change the address on the letter so it can be sent to the correct address.
Request notification from the post office of the new address if your letter is forwarded through the "Address Correction Requested." The post office will notify you of the person's new location for a small fee (usually less than a dollar).
Search for the person's new address in the white pages of a phone book, or online via the white pages search engine. This works well if you know the city that the person moved to. If you do not know the city it is harder to find the person's information via the white pages.
Keep a proof of purchase to show that you requested that your mail gets forwarded to the person you are sending a letter to. Document each technique you used to locate the new address. This way you will remember what worked and what did not work. Birth dates, middle names and other personal information can help you find the person that you are searching for.