Messeage to the readers in the book "pretty little liars"?

The book is about 5 best friends, who do everything together, and Ali is the head of the group who knows everyones individual secrets. Ali ends up going missing, and the four other friends go though harsh times, and get these emails, and texts from this girl named "A". Tree years later, they find ali's body, that has been cremated under a tennis court for 3 years. If you read the book its easier to answer.. Please Help :)