I have just finished Still Missing and thought it was a wonderful book. Not terribly happy subject matter though, it is based on the Etan Patz case (1979) and was published in 1981.
The book is based on the psychological unravelling of a mother (Susan Selky) after she discovers that her six-year old son has gone missing, and that he did not actually arrive at the school after she waved him off. The initial investigation is gripping, and your heart goes out to Susan as she reviews the quality of her relationships with friends and family when they cannot cope with her determined belief (hope) that her son is still alive.
Certainly worth a read - but, be warned .. it made me cry several times!