There's three separate reasons why you're screwed:
1) You have no recourse because you can't report the theft to police.
2) You have no recourse because you can't identify the operator, he's anonymous, which means he's also hidden from you.
3) You have no recourse because you can't undo your transaction.
As a good rule of thumb, only perform transactions in bitcoin doing legal things, that leave you at least with some recourse in case things do go wrong. And if you sat there, holding your coins, thinking "oh, I'm just gonna buy drugs with them, what could possibly go wrong", you seriously shouldn't have bitcoin, they're not good for you. Oh, and drugs are also not good for you, so please don't do them.