Pretty Little Liars Series by Sara Shepard

Pretty Little Liars Series – Four girls—Aria, Spencer, Hanna, and Emily—are tormented by a mysterious figure called “A” who knows all their secrets. As they try to uncover who “A” really is, dangerous lies, hidden pasts, and shocking twists threaten their friendships and their lives.

Total 16 Books in the list - 

• Pretty Little Liars
• Flawless
• Perfect
• Unbelievable
• Wicked
• Killer
• Heartless
• Wanted
• Twisted
• Ruthless
• Stunning
• Burned
• Crushed
• Deadly
• Toxic
• Vicious