How to Find an E-mail Address by Facebook IDby Kristie Sweet
With 1 billion members active each month, Facebook is a good source if you want to find friends. Users can receive private messages via a Facebook email address, but they may post alternative emails in their contact information as well. Locating users' email addresses requires finding their Facebook pages, which can be accomplished through a search from a user ID, also known as the Facebook username. Facebook makes it easy to search for friends and find ways to contact them.
Navigate to the friend's Facebook page. In the address bar at the top of the page, type "facebook.com/" (without the quotes) followed by the friend's username, such as "facebook.com/jane.doe6." If you do not know your friend's Facebook ID, you can search by name. Type the person's name in the search box at the top of any Facebook page and click on "see more results" at the bottom of the results when it appears. Then select your friend from the list.
Click the "About" link under the friend's cover photo.
Scroll down until you see the section called "Contact Info." Any email addresses the friend has associated with the account, including the Facebook email, appear there.