If you put them in a club with "any x" as their hangout they will congregate any time you go to venue type x, if that helps.
I used to see the same sims out all the time, a mix of mine and some premades, but there's been a shift as my sims have aged. The YAs are more likely to show up at nightclubs, for one thing. It is not at all uncommon for my families with kids in the child stage to show up at restaurants and then stop when the kids grow up. Active sims are more likely at gym lots but I haven't specifically noticed that kind of connection with other traits.