"Hit me up" could have a few different meaning: 1. "It was nice talking to you, hit me up later when you have a chance". In this context, "Hit me up" would mean that he/she wants you to contact them again at a later time when you have a chance. OR 2. "Hit me up with some of those donuts". In this context, it means: I would like to have some of those donuts that you have/eating.

The phrasal verb "hit up" means request assistance from someone. In the case of a pronoun as object, the pronoun goes between the two words of the phrasal verb.