Every social situation in which individuals are voluntarily taking part – sometimes they might also be coerced to do so by vocalized or non-vocalized social regulations, sanctions or force – leads to the formation of a social structure. Even in short everyday interactions, sharing an elevator for example, these mechanisms are visible.
Of course, one could argue that the trained eye of a sociologist might only see what it wants to see. In these cases, the examples have to be extraordinary, like pilots and other airport personnel building mobile colonies on airport parking lots. They even have a mayor, problems with prostitution and unsolicited residents.
Now if that isn’t convincing, i don’t know what else is.