Someone to Run With by David Grossman.

A boy runs through the streets of Jerusalem trying to find the owner of a
lost dog. A girl runs through the underworld of Jerusalem trying to get her
brother back from the clutches of the seedy characters who are exploiting
him. And, eventually, find her dog.

The book is a bit slow to start out with, but it picks up about a quarter of
the way in and just doesn't stop. It sometimes comes perilously close to
falling in the TEEN DRAMA! category, but it manages to stay on the realistic
side of the line. Sweet Valley High this isn't. The characters are
beautifully flawed and realistic, and the plot is very plausible for a
thriller/mystery/adventure. The book gets uber bonus points for having a
character who's a shy geeky loner, and NOT giving him a kind, loyal,
omnipresent soulmate of a best friend. (Because if you have a kind, loyal,
omnipresent soulmate of a best friend, then you are NOT a loner). The
ending has so much cliche potential, but the author manages to avoid it by
ending the story at an appropriate moment and leaving the rest to our
imaginations.

I'm told the translation from Hebrew leaves something to be desired, but
I'm not at all qualified to evaluate that. Otherwise, very enjoyable, hard
to put down, one of the best books about adolescent characters I've ever
read.