I have loooked around in my home town (Daughter is 8. That is the age where our police some time meats them drunk in parks and on beaches. Let me say that I keep a little eye on her and encourge her to spend time with her family rather than having her running around without supervision.)
In my town they hang out at the Internet cafe, at the bus shelters by the station, the pizza joint and finally a certain drug-store, if they are not involved in sports. (We have soccer, swimming bath, badminton, tennis, various gyms, cycling and athletics clubs) so if you have slightest need to get sweaty, our city can mean your demands. Outside sports our city do also have association for everything even odd things like grownup men and women playing with matchbox cars. So even Nerds are accepted. (Denmark have over 70,000 assocations for more and less odd things).
Where do your youth meet if they are not involved in sports? Maybe it is there, where the poster should hang.