I find that community groups that started before Facebook, or have avoid Facebook, have done better/do better. With Facebook you get locked into using the platform and the group doesn't grow. In fact the group just get worse over time as original member leave. Content and group information is locked into the platform.

Even if a group just sticks to using email, it is better over the long term. People in the group are forced to take on responsibilities of maintaining the email list and content. Passing that information on as they leave. You can also scale up the organization, make it more formal. Start collecting dues, and paying for server space. People take pride in their roles, and the organization.