A person who always responds to another specific person's (i.e., the "target person") facebook status updates and links, typically within the first few minutes of it being shared.
The facebook groupie either 1) intensely romantically likes the target person, 2) wants to BE like the the target person, or 3) wants to be accepted by the target person's group of friends. The facebook groupie is often among the very first to respond to the target person's status updates/links and very rarely let's a target person's status update/links slip get by without a response.
They are often unaware how embarrassing, lap doggish, or futile their behavior appears to be. While the facebook groupie is typically of the opposite sex of the target person, facebook groupies can be the same gender as the target person.
Caveat: The term facebook groupie does not extend to family members or significant others. Therefore, you cannot be a facebook groupie to your husband/wife boyfriend/girlfriend, sister, brother, cousin, etc.