Well, usually people will use forums as a secondary thing. Most of the time there will be a game, video series, or some feature that they use and then go on the forums to discuss it.
Forums generally have dropped off since there are so many chat/talking features out there now for people to discuss topics on.
Example: Twitter, Facebook, Skype, YouTube, Google+, LinkedIn, Instagram...ect
Possibly if there were a main forum focus on a topic such as a game the 4M takes part in or makes. That's just an example. It can pretty much be anything, but it needs to specialize in something first and then users can make use of the rest of the diverse topics.