"Cathy's Book : if found call (650)266-8233" by Sean Stewart and Jordan Weisman. Running Press, 2006.
Cathy, a senior in a Bay Area high school, journals about events that happen to her after she starts dating Victor. He suddenly dumps her, and she and her best friend, Emma, do their detective thing to find out why. They become involved in murders, burglary, kidnapping, and laboratory experiments, reminiscent of edgy, alternate reality internet gaming. Cathy's book is illustrated copiously with her sketches and doodles.
The jacket blurb indicates that the authors are, in fact, PC Game creators (MechWarrior, I Love Bees), and invites readers to "Read. Explore. Investigate. Examine the Clues. Call the phone numbers. Access the websites. And when you're done, you'll know that the teen novel will never be the same again."
I didn't explore, investigate, or call the phone numbers, but if anyone does, I invite you to post what you find out in a comment.
(Original post at "Bibliog"; used with permission.)