"Frankie, I think. He was right next to me, just making a joke, and then it was like something yanked him away. Yeah, it was him. Definitely him." -Winston confirming Frankie's fate.
Frankie was a former Glader who appeared in The Scorch Trials.
Biography
He and 20 Gladers managed to escape the Maze but he was the first one killed in the tunnels by the head consuming metal balls.