Yes I've read it and yes I think it's definitely appropriate. It was on the summer reading list for my kids last year (before 10th grade) so while there are some heavy themes in it - the narrator has cancer - there is nothing wildly inappropriate. There is one mild sexual experience in the book but it's not graphic or really highlighted or given a lot of importance, kind of just glossed over and in the context of the book, not objectionable.
It's a very, very sad book. If you're unsure, read it yourself. I read it in a night last year. I tend to read my kids' summer reading books because I like to read and they're right here in my house so naturally I have to feed them to my brain :-) As an added bonus, I can ask them questions about the books to make sure they actually read them.