I'm no master of PayPal, start a dispute and be honest with PayPal on what happened, I'd wait for other people's opinions first though before doing anything yet.
Also make sure if the person who scammed you is on Sythe, make sure you file a scam report.
Seriously, all you do is appeal the transaction and say you never got the item. Dont go down the ebay route as you have to provide some evidence. Make up some stuff about how you bought a computer or something from a local shop (so you dont have to provide shipping address) and whatever you do, please please please don't mention runescape or intangiable goods (which are goods that do not exist in reality like GP)