A person --other than a family member, significant other, or spouse--who always and consistently comments or likes another friend's facebook activity. The facebook groupie consistently engages and interacts with his/her idol on FB and his or her idol's pictures, comments, and other FB activity. Often the facebook groupie is the first to comment on a person's status update.
He comments on every on my every post. He is my facebook groupie; or
She obviously likes him, because she comments on his every picture or post. She is one of his facebook groupies.