Are there any legitimate companies that I could work with to sell my timeshare?

I got a question from MH on Facebook. He wants to know if there are any legitimate companies that can help him sell his timeshare.

There is an organization called the Timeshare Users Group. They are known to be the first and largest timeshare owner network. When you visit their web site you find numerous articles, tips and advice on everything related to timeshare ownership including buying, renting and selling your timeshare. They will even let you advertise your timeshare on their free classifieds section.