The Perfect Stranger by Megan Miranda is the book following All the Missing Girls, although these two books are totally unrelated to each other.
The Perfect Stranger just came out in April of 2017. I purchased it for $2.99 on my daily BookBub email in one day in May when it was on sale.
This book centers around Leah who is a girl trying to escape a scandal in Boston by heading to Pennsylvania to live as a teacher with her friend Emmy. Emmy disappears a few days after there is another woman who was assaulted found by a lake.
Leah is alone and scared and falls into a romantic relationship with a local policeman named Kyle. Flashbacks to her encounters in Boston are examined, and the reader gets a glimpse into what happened to Leah in Boston.
The only reason I gave this 3 stars instead of 4 stars is because the ending is abrupt and did not give the plot justice.