On withdraw, bitstamp should give you an id which you can use on eitherscan.io (i think it is) to track - like you would on blockchain.info for BTC (also think blockchain.info just added eth). Check your withdraw section at bitstamp. It also could be your withdraw was cancelled for unknown reason, if so check your balance or email support.
Theres really an id shown regarding on your withdrawal request and its really just like on blockchain transaction. You would able to see this if the transaction have been processed already and as being said there are some cases on which it might have been canceled or didnt processed for a certain reason.