Did they leave you feedback after the initial transaction? If so, it might give us an idea of the current username. If they did, don't put the username here as that's against forum rules, but you can tell us which feedback it was and we can go and have a look.
Unfortunately, I hate to say it, but you probably won't get your money back now. Not unless you know where they are and you could try and get them through the small claims court (very expensive though).
In future, if you have any issues like that, always open a dispute through PayPal. Don't post anything back until PayPal tells you as they will give you the address that you must post it to. By doing it their way, 99% of the time you will get a refund. By just posting back off your own back, it's very easy for a seller to just disappear and you've not only lost your money, you've lost the item too.
