I am not familiar with the website you're asking. But if they're already gone, who are the people that you will chase? do you know them and you have valid proof that they've stolen money to you?
In this case, you should be consulting a lawyer that's expert on this kind of cases if you want to pursue a case but as I've said, you have to provide to those things.
Can they just dissapear into the thin air with our coins?
Sadly, yes and they've just did it.