Poloniex can be unreliable and their support takes weeks to respond (if at all). I have had numerous transactions get "stuck" but have not been ripped off yet. Did you use a memo on your deposit? If you did then you just screenshot their deposit address memo and get the block number of your transaction, raise a support ticket and they should credit it (eventually).

I've got BitShares stuck there for a few days now and the wallets are down. I'm just trying to be patient and using other exchanges.