In one brisk move, you turn and catch the hand that was rifling through your pockets. You grip their wrist as they jolt back in shock. You lock eyes with the owner of the hand: a young woman - no, definitely still a teenager - with bright eyes full of bewilderment. A new, rather innocent face, that you've never seen around before. Her clothes are modest and worn, but not battle-worn or pirate-like at all. She's clearly out of place here.
"You trying to tickle me?" You ask sternly.
"Uh, I, no -" she stammers. "I-I was just walking by. Let go."
She tries playing off her surprise to your action as though it was random and unwarranted. She attempts to pull away again, but your grasp remains. Your companions and other nearby patrons start to notice the disturbance.
She's clearly out of her depth, a little mercy wouldn't hurt. You can let this slide, and maybe have a little chat to find out what a kid like her is doing around here in the first place.
Tough love. If this kid is going to survive around here, she has to learn the consequences of actions. Exposing her ought to scare her straight. With any luck, she'll take it as a cue to abandon this wretched way of life.