Problem
The most common word used in order to describe shared online places/ interests is community. I believe this is the wrong word as it implies a level of investment that far exceeds that of an online "community", in order to participate in a community in real life you need to actively contribute emotionally or materially, furthermore there is a much stronger bond than an online "community" as you have gained trust within the community for the struggles you went together. On an online "community" you could easily leave and abandon post and so can everyone else. The price of entry in an online "community" is also much lower (being practically null).
Solution
As such I prefer to refer to online places/interests as congregations. A congregation is simply a group of people who share the same interest/belief/site of residence. This terms fits much better as it accurately describes the low investment level that is found within online congregations.