I can't think of word(s) to describe a twitter group of people who haven't met but have an indirect familiarity with each other. I thought of clique but it doesn't seem to fit a loose indirect group.
John hesitated to contribute to a twitter conversation on a technology subject as reading through the conversation it felt like an exclusive boys club and he was worried his contributing could make him see like an outsider which could tarnish his public image.
Background: I find with twitter the people who converse with each other in conversations in a technical topic use humour or snappy one liners and have this unique language of their own. They have never met each other just follow each other due to a common interest. It is similar to a boys club or exclusive club but not really as they have never met in real life but follow each other so know the unique behavior and what twitter tweets the other would engage with. A new person wanting to give his insight in a current topic of conversation might ask a logical question but because it isn't in the same style, format or historical sequence the person is treated as an outsider or twitter shunned, excluded or treated as a person not part of the group in their tweet responses.