Running Away: what's going on and the need for a re-entry plan

While I was on my walk this morning, a young man who looked to be about 19 showed me a picture on his phone of his kid brother, and asked if I'd seen him or his bike. Apparently his 13 year old brother decided not to come home yesterday after his mother told him she'd be confiscating his phone.The older brother was so worried that he'd been up all night trying to find him, and was now looking for him in the little wooded area near our neighborhood.

Surely there's a lot more to this particular situation, but in general, I wonder what's going on at home when kids decide to run away?