If you own a forum and want some activity, you can do the trick I'm about to mention. Remember you need a few active member for this to work and obviously active marketing.
All you have to do is create a thread with title "Last post gets SOMETHING" that something can be $100 some good tag or anything that's valuable for your audience. Just create the thread and see people replying to thread 24/7!
If you've been actively promoting the forum it's unlikely you get to pay the winner because people will always keep replying. If if for some reason you see nobody has replies to thread in a while, pay the winner and use his testimony to create new thread and get even more activity going!
I hope it helps!
Any questions? I'm here!