Promote it where your target audience is hanging out. Social networking sites would be the big ones. Make sure that it's functional and has some topics running before diving into promotion though, if it's just an empty forum when someone finds it, chanses areit wills tay that way.
If you want to free promotion I guess facebook is the ideal spot. Just add some friends and message them saying "Hey! Let's hang out at www.YOURFORUMURL.com" Otherwise, I guess advertising on blogs frequented by teens would be great.
MySpace's market is oversaturated already. hardly anyone reads any bulletins that look like advertising.
Yes, that's the problem I have. MySpace and Facebook have an awesome target audience, but there's really no good way to reach them. Any other ideas? I have a $500 advertising budget.