If you want teens to stop hanging out at the Pizza store after shabbos, give them an alternate place to go without and learning or chessed obligations
Give them a place to go and shmooze with their friends and maybe have the pizza go to the place. Like a Beis Yaakov gym for girls and maybe the gym of a yeshiva for the boys.
If you want to stop it, You need to give an alternative choice and not one teens will reject because of rigidness. They are not learning or doing Chessed at the Pizza shops either