What can I do to get my money back?

Unfortunately, since this guy moved out of state, you are likely to have a very difficult time getting any money from him, especially if (as I suspect) you didn't get a written agreement from him to repay you. Even if he were still in Pennsylvania and you would sue him in small claims court (since this amount is well under the threshold for filing with a district magistrate), without a written agreement he's likely to argue that you gave this money as a gift, not a loan.

When you say you haven't been able to contact him, but you know the person with whom he's living, does that mean you have his new address? If so, especially if you think this guy could return to Pennsylvania at some future time, you could file a claim with the magistrate in the area where he lived at the time you lent him the money. You'd have to ask the magistrate's office to serve the complaint by mail; he could always refuse to sign for it. Even if you're successful in getting a default judgment against him, you still have to collect on it, and since he's in SC that's unlikely.

You best (nonlegal) option might be to contact his mother (especially if you knew and got along with her while you were dating her wonderful son), explain the situation, and ask if she might tell him to contact you so you can work this out. It's a VERY long shot, but you have about as much a chance of success with the personal route as with the legal route given your facts.

Moral of this story: lending money to someone you date -- and especially doing it as a cash advance on a credit card -- is almost NEVER a good iead. And it seems that this usually happens to women whose boyfriends take advantage of their affection (I know guys must give money to their girlfriends too, but all the cases I know involve women taking the financial hit).