Social media is eclipsing forums (and websites to a degree) just like the web eclipsed bulletin boards 10-15 years ago. You could still make a new forum successful for sure if you have enthusiastic visitors, but the momentum is against them. A website with integrated social media (cross-posting, commenting, liking, plus-ing, pinning) seems to be a successful paradigm right now. Either way, you will almost certainly need to be engaged and producing content and/or participating with your readers to be successful (financially or otherwise).
Forums will never be replaced by social stuff unless they do something to conquer. Q&A section of linkedin was recently shut down
It would be better to create a forum with related topic. It will need more energy and returns huge valuable/ethical visitors and hence increase your profits.