Harry Potter!
Most of the important characters are young, they start out at 11, and the series was HUGELY popular, among both kids and adults. I think popularity has little to do with the age of the characters. It's more about how well anyone can identify with the characters. We've all been young once. We all remember the awkwardness around members of the opposite sex, being clumsy, feeling like the world is out to get you, other angsty things.
Make your characters realistic, identifiable, and, as others have said, a little mature for his age, and you'll be fine.