[Mad Dawgg]

"It could be also a prank, or a setup for extortion, with her "big brother" hiding nearby and ready to accuse you."

Or worse. A setup to get the target down on the ground checking on the poor girl while the thugs move in and mug you or some new variant of the "knock-out" game.

And so on and so forth...

[reformedliberal]

So, use that Smartphone and call 911.