I just found out about another book on missing people that was published last year: Clueless in New England: The Unsolved Disappearances of Paula Welden, Connie Smith and Katherine Hull, by Michael C. Dooling. I put in a library request for it, since its publisher did not see fit to send me a surprise free copy.
Katherine Hull is no longer missing; she was found dead seven years after she vanished. The whereabouts of Paula Welden and Connie Smith are still unsolved mysteries, however.
The Charley Project Blog 