Instructions
Locating a Gamertag Through the Controller
Press the "Guide" button on your Xbox 360 controller. The "Guide" button is the large silver button in the center of the controller with the "X" on it.
Select "Friends" and press "A" on your controller.
Scroll up and down through the list of friends until you locate your friend's gamertag. Friends here are displayed with their gamertags only.
Press "A" to bring up that friend's profile. Here you can send him a text or voice message, or view his bio.
Locate a Friend's Gamertag Through the 360's Main Menu
Navigate to the "My Friends" menu on the Xbox 360 Main Menu screen.
Scroll left or right through the list of friends. Friends in this menu are displayed with their gamertag and avatar.
Press "A" to load your friend's profile when you have found his gamertag.