I've been getting this question for the past 48hrs, and I've been ignoring the question as I thought it was simple to search and find the answer, that answer being blocktrades, but after realizing today that blocktrades is not currently the answer, I made this video.
NOTE: Steem and Steem dollars are two different markets on bittrex.com, so do not send your steem dollars to the steem market, search for the steem dollar market on bittrex and send it there, this video does not make that clear.