It needs to be shut down. It sounds like he has been dismissive of your attempts to talk to him about it, therefore I would escalate the consequences. You can warn him first, take him aside and say I do not want you to physically touch me in class, if it happens again XYZ (goes to admin).

I always interpret this kind of behavior as young men/boys touching a female, realizing it makes them feel warm and fuzzy inside, and wanting to do it more. Sometimes they realize they need to be subtle about it and do things like you are seeing. Example I had a 14 year old boy running around hugging girls and not letting go as a 'joke.' I don't think we need to label these people predators or whatnot they just need to learn boundaries before it gets worse.