Who is Thayer Vega from The Lying Game and what is their importance?

Thayer Vega is the brother of one of Sutton's best friends, he has been missing for weeks by the time Emma enters the picture. There is evidence that he and Laurel are more than friends prior to his disappearance.

Thayer Vega is basically Madeline Vega’s brother and someone who was connected to Sutton before the main events of the story. By the time Emma shows up and starts pretending to be Sutton, Thayer has already been missing for a while, which makes him kind of mysterious in the plot.