Katy Perry had a whole host of famous friends to help her celebrate the premiere of Katy Perry: Part of Me in LA last night. Justin Bieber and Selena Gomez, who showed off her new hair extensions, stepped out together for the event, as did Carly Rae Jepsen, Kathy Griffin, Raising Hope's Shannon Woodward, and Seth Green. Katy performed for a crowd of fans before the movie's screening, but the fun didn't end there. Katy, Justin, Selena, and Shannon met up with Robert Pattinson at the Chateau Marmont to party into the evening. When the bash was over the whole crew was spotted leaving the hotel and hopping into Justin's custom Mercedes van.