Serious question though, what difference does having an adult around make? Usually they'll let teens get on with it. They won't sit supervising directly, they won't be in the room.
They might smell smoke or something, they might make some kids curb their behaviour instinctively, but they might also just totally check out and ignore it all.
And if there are issues, teens are hardly likely to run to Jimmy's mum to say "oh no, Jimmy did/said this, please come and tell them off / call my mummy" are they?
It would be better to train them into being confident people who know the risks, or training them into how to get out of situations with ease.
If you're worried about them being stuck in a situation they can't get out of, you could even have some little codes set up between you - a text from you saying "was it the blue shoes or black ones you wanted?" or something, and a "blue/black" reply meaning something back to you?
I dunno, that could be a totally rubbish idea, but being on their side as they venture out seems better than just keeping them locked up seems better to me IYSWIM.