Evan's only friend is Ariel.
Ariel is gone.
But what happened to Ariel? And who is sending photographs of Ariel (and other people, initially unidentified) to Evan?
David Levithan's novel Every You, Every Me incorporates photographs by Jonathan Farmer. While Evan scrutinizes each and every picture and note he receives, it is worth remembering the tagline on the cover of the book: "A picture is worth a thousand lies." Readers have more than one mystery to figure out here. Evan's first-person narration is mostly directed to Ariel, addressing her from the get-go, using "you" frequently and really pulling you into his story and in his thoughts - but do you think he's a reliable narrator, and do you think he had something to do with Ariel's departure? Your opinion may change from chapter to chapter as more backstory is detailed, and it may change again when the truth is finally revealed in the final chapter.
Kudos, David Levithan, for incorporating Zeno's dichotomy paradox into your story. Thank you.
My favorite Farmer photo in this book appears on page 228 - but don't you dare turn to that page until you've read pages 1 through 227. It won't mean as much if you look ahead.
I also posted this review at GuysLitWire.
If you like Every You, Every Me, you should also read As Simple As Snow by Gregory Gallaway, which I've talked about here at Bildungsroman as well as at GuysLitWire. Snow also employs a teenaged male narrator, a missing-in-action vivacious female friend, and mysterious elements.