Anasazi

'Anasazi', sequel to 'The Thirteenth Chime' by Emma Michaels:

One year ago, something happened to David. Following the only clue he had he headed out into the desert. Now he has asked me to come see him. But when I arrived, he was gone. The people in town claim they have never heard of him and everyone wants me to leave.

But I know he was here and he is in trouble.
He can't survive out there for long.

Can he?

David. I will find you.