I love creating websites.
I love art.
I love video games
I love video production.
Mainly, those are my hobbies but I can't justify the time creating them if no one will come talk to me on it. I know this is a very generic questions, but taking these passions what kind of specific niche could you recommend? I did have a hard time finding any real good video creation forums.
If you want to talk to other people about that niche, then do as @professorrosado suggested and launch a blog in that niche. And then go join whatever existing forums are out there in that niche and talk to people that way too.
If you want to create a new community where people are going to discuss that niche (a.k.a. a forum) then you should first assemble a team of people that will serve as the initial contributors/moderators/members/content generators/discussion starters etc.
If you are thinking you want to launch a forum by yourself as a means to make money with a website, then I strongly recommend you don't bother. It is one of the hardest ways to make money with a website if you are starting completely by yourself.
Also, just because there are already forums that exist in the niches you want to work, don't let that stop you from starting one. If you have an excellent team in place, then you can start a successful one in just about any niche where there are lots of people talking about it. The key is to have the right team right from the start or at least very early on in the launch process. Otherwise it will be an unbelievable struggle. Just my opinion based on my own experience.