|I've read this book countless times since high school; it's one of my top three favorite books. Ethan Shumway is sixteen when he disappears - literally disappears: his younger brother, Philip, sees Ethan at the end of the driveway one minute, then he's gone. The book is Philip's searching for (or "not-finding", as he calls it) Ethan.
There is something about Reiken's writing that makes the whole story vague and mysterious, yet complete enough to be satisfying, regardless of what the resolution may be. It's on my shelf of Favorite Books and has been there since I got my own copy. It's a beautiful, little-known book that you should read.