Gangs are an organized group of assholes who cooperate usually in criminal activity. Gangs are primarily an extroverted activity. In order to join a gang and to thrive in a gang you need social skills, because it is a group activity. Gangs also appear and are maintained as a form of protection when one lives in a rough neighbourhood or a county jail.
Gangs are prevalent throughout the western world. The reason why gangs thrive so much in the west can partially be explained by societies coddling of extrovertedness. If society did the opposite and normalized and coveted introvertedness, gangs would immediately look suspect, they would invite more suspicion and seem out of place.
Since introverts overall are aversive to collectivism, gangs by definition do not contain introverts; rather they're a group of extroverts.