Hollywood stardom is a fickle thing. One day a star can be the center of attention, and the next he or she could be considered passé. Mischa Barton was a fixture on the hit show The O.C. and now flies under the radar. Freddie Prinze Jr. seems to have fully ditched his teenage heartthrob days and works for the WWE network! See which stars have gone M.I.A. – and if it was intentional.