Hi, welcome to the forums. Plenty of people still play JJ2, which you can confirm by yourself by just starting the game, going online and seeing how many people are playing it! I'm not sure starting a forum about it would have much use, though, as there's a fairly well-accepted central forum already (you're on it right now) and also a more multiplayer-oriented forum at http://jazzjackrabbit.net. That seems plenty for a game this small.

As for dedicated servers, there's no such thing yet, but some people have run 24/7 servers before. Searching the forum for "dedicated" might still yield some useful information.