Steem withdrawal/deposit has been stopped for a really long time on Poloniex now. A lot of people have their Steem stuck on that exchange, currently the Poloniex Steem account has 24,370,085.788 STEEM and 1,345,329.908 SBD which estimates to around US$32,127,447.70, that's a lot of money and all of it belongs to different users.
I think the Steem team should try and get an update from Poloniex and maybe try to get the withdrawals and deposit of Steem and SBD working again, because a lot of Steem users are affected by this problem.