The Best way is that contact Apple and provides your info then you got solution
Apple can't do anything about it. Reason being is if the thief ever took the MBP in for servicing and a note was on system about it being stolen, the thief could say he recently made a private purchase from the guy who reported him. There's no way to prove that it wasn't a legit purchase. Who knows if the guy that sold it to him got angry for some reason and maliciously reported the computer stolen when it really wasn't.
Apple cannot confiscate someone's computer or get the police involved unless the computer was stolen from their store.