My final guesses for A.D.
Spencer’s Twin: A.D. = Avery Drake. I won’t get into this one too much because there are so many clues but I just wanted to mention how it was only Hanna and Emily who saw Avery’s friends, they never saw Spencer.
Melissa: There are a lot of clues pointing to Melissa since the beginning of the show. I’ve seen spoilers saying that A.D. is two people, a male and a female. Maybe it’s her and Wren is helping her.
Ezra: He stalked the girls and had a lair so he could write a book? That would also explain why A.D. wanted to protect Aria from going to jail.
Lucas: He could of easily build the game board and he was friends with Charlotte since they were kids so he would want to know who killed her.