If you're struggling to keep the forums moderated, you might want some volunteers.
The typical approach here is to advertise for volunteers to moderate the forums. You might get a few, they will last for a while and once they get bored you will need to recruit another batch.
The better approach is to create a broader, more exciting, role. This role encompasses a range of fun tasks but also includes forum moderation on key topics. You're more likely to get volunteers that write a weekly opinion column, find experts to participate in discussions, arrange activities, provide expertise feedback and moderate forums topics.
It sounds like a better role.
If you want volunteers in your community, put together volunteer positions that sound fun to do. Make people apply for them. Not only will you get more people you will get better people and more work out of your volunteers.