Some are formed organically as like-minded people naturally find one another. Others are formed by brands or organizations around their products or services.
I've been a part of all kinds of communities over the years.
Doesn't matter if it was a Usenet group formed around Prince bootlegs or a private group on Facebook on social journalism. At some point the community was formed and then it became what it is today based on the members of that community.
Where people fall down all the time is that they think they can control a community. The most successful ones can be guided and directed, but at the end of the day the members are the ones that will determine if it is what they want or not.
Especially in today's world where we are only a click away from the next distraction/destination. Where we spend our time online must provide some form of value to us.
Recently, I was told what I chose to share in a community was not appropriate. I laughed a bit because once again I was watching someone make the mistake of thinking that just because they brought a group together that they could control how we interacted with each other.
In this case it sparked a conversation of other members helping each other. Exactly what a community should be all about.
The best communities want the members to interact with each other. Get to know one another beyond why they've assembled. That is how real friendships and lasting relationships are formed.
Being empowered to ask questions of the gathered crowd and collectively share knowledge around the given topic is the glue that will keep the community going.
I'm not an anarchist and know that you need rules and enforcement in the world to keep the basic sanity of life around you. I'm not saying otherwise.
This is why the role of a community manager is so critical. They are there to be more of a cruise director than a drill sergeant and help keep the community from going off the rails.
No matter what kind of community you set up, it is the members who will determine if it grows and thrives. How the creators interact and work with those members is vital.
Let them interact. Let them share. Encourage them getting to know one another better.
It will help you and the community in the long run.