Depends on your point of view.
pejorative: gang, rabble
approving: club, society, association
As far as I know, in Scotland, gangs are generally called "gangs". A notable exception is the Burns Society
If a bunch of "neds" are vandalising your neighbourhood, you might well refer to them as a "gang". In the 1970s the Edward Heath Conservative Government referred to the Northern Ireland IRA as a "murder gang". However, I don't think that either the neds or the IRA would use the word "gang" to describe themselves.
Maybe members of a marginal informal grouping would call it a "club" because it sounds nicer?