The phrase used to describe someone you are friends with on facebook but don't actually know personally.
Guy 1, looking at guy 2's facebook page: Duuude, who's this hot chick Sally Smith on your facebook? Hook me up!
Guy 2: I don't know her, she's my cousins friend.
Guy 1: ohh, a facebuddy. Still, she's got some shweet legs.
A guy who is your friend with whome you ride his face
This guy paul was my face buddy and then I made him my boyfriend
A person who looks like you, whom a mutual friend or acquaintance has photographed or tagged on social media. Or mentioned. Or put you in contact with. Whatever. You then confirm the verisimilitudinousness and end up being buddies. What could be easier, or freakier?
S: The pool attendant at my gym looks SOOOOOO much like you. I want to take his picture.
H: You should. I'd like to have him as my Face Buddy.