Someone who "likes" or comments on practically every facebook post you make.
"Why does that dude keep commenting on my status?" "He's a facebook leech."
a "friend" who systematically goes through your facebook friend list and sends friend requests to every girl on there using you as a mutual friend: even the girls you may have had one awkward date with twenty years ago that the leach has never met or heard about.
dude, why are all my old girlfriends now listed on HIS facebook page? he's never met them and they live ten states away... that dude is a facebook leech.