How can I increase user participation on my forum?

Hi people, please I have a forum that has good content but a very low user participation in the form of postings and replying to posts. Even when I set up a system to reward posters, I still get very low response from them. It is also difficult to get new members to register as they just use the resources on the site and leave. How can I make them participate more on the site? Valuable suggestions will be appreciated. This is a link to my site for reference https://classhall.com/discussions