Perusal of a facebook "friend's" photos in an effort to catch-up on their lives...usually because communication with that "friend" hasn't occurred for a substantial period of time.
"Have you talked to Catherine lately?"
"No but I creepbooked her photos and I think she's moving out of her apartment soon."
Actively looking through another person's Facebook in order to gain info, spy or to stalk
After a breakup:
ExBF: So I found out you went a date last night...
ExGF: How did you hear that?
ExBF: I saw on your Facebook
ExGF: STOP CREEPBOOKING ME!!!