Many are free,but with a few you could eventually get a bigger crowd
Try to find some maid just for mybb
Facebook,twitter connect,StumbleUpon is a good example of mixing social networking and social bookmarking, although the social networking side has gotten a bit more difficult since the new StumbleUpon update. StumbleUpon’s main focus is discovering websites that others will be interested in and adding them to your favorites. You can use StumbleUpon purely for social bookmarking by thumbing up sites to your favorites – just be sure to tag your favorites with keywords that you will remember to search for later, such as having a collection of WordPress themes or Twitter resources. Also, you can go a bit further by adding a review – like your your favorite part of the article – as a reminder of why you liked the article when you go searching for it later.
StumbleUpon also allows you to connect with other members who have particular interests and share sites with them through mutual subscriptions. In the previous version, you could request to be friends with someone and, once they accept, you will be mutual subscribers. Now, the process involves either messaging someone asking to exchange subscriptions or subscribing to someone else first and letting them know, in hopes that they will subscribe back to you so you can share pages with each other.
The more of these that you have installed,the higher your page rank will be,and the more folks will come.