The Lucky One by Lori Rader-Day

A perfect example of what makes a good thriller - the pace is perfect (speeding train), the characters are believable (flawed and human) and it makes you question every new bit of information at the same time the protagonists are (like a good Agatha Christie book). As a child Alice was a victim of a brief kidnapping that ended with her being found quickly, making her one of the lucky ones. She is now obsessed with an online group that looks for clues and hopefully finds missing people in addition to her job at her dad's construction firm. One day she sees a face that looks way too familiar and the story snowballs from there. Lori Rader-Day knows her stuff so prepare yourself to fall down the rabbit hole with Alice and get nothing else accomplished until the last page.