When consulting, I find many organizations work backwards.
They decide what features they want in the community and then try to figure out how to persuade members to use those features.
This is backwards thinking.
You should begin with identifying the motivational drivers of your audience and then add features based upon that motivation.
What are the key drivers of participation in your community? Is it the need for achievement? Self-efficacy? Power? Money? Recognition? Fear?
Now, what features would help members achieve these goals?
You shouldn't decide to add a feature without having a clear motivational driver underpinning its use. It's far easier to create and changes features than it is to create and change motivation.