Either drop DNN and try out Community Server or vBulletin as your friend has, or work on providing more of your own content. Websites require original and new content in order to attract return visits. Websites that rely solely on the content produced by visitors can go dead pretty quick.

If you went looking for cool content every day and added it, people will come and look at it. Make sure they have a convenient way of talking about the content or rating it etc. If there's nothing new other than their own posts then they probably won't.

Another tactic I've seen used on sites that have to build their content from visitor discussions is to purposefully create controversy. Become a troll... say some sports team or some band is better than another... or whatever. Start a jesus or a loonix chat perhaps... there's no end to the things that people want to spout off about. Have a competition... somethingawful.com does a weekly photoshop friday competition where forum users alter images to a set theme.. usually something horrendous, but keeps them coming back every week.

Let us know how you get on.