I would suggest run Contests, like x Amount of relevant posts in different categories and you could win X Amount. Thats what i have been doing.
Vudu magic, gun point nothing would work unless you work to get people a reason to post. There are tons of ways establishing a forum. All requires years of hard work. Unless you can commit to that sort of work, its time to call a quit now. Here are some tips you might find helpful: Be online on your forum as much as you can Participate on other forums on similar niche, daily basis. Make posts, dont spam. Use signature. Add good content daily basis. Use social marketing. Good luck to you.