Hi and welcome to the forum
If you want to add a friend that's not in Facebook, the only way to do this is to search him through associations and check if the blue "Add Friend" button appears. If it does, which is a very rare occasion, this means that you're in the same server.
However, I think there should be a more "direct" way to add someone as a friend in-game. Would you like that?
Good luck this season,
Milpol