Katy Perry celebrates with Pattinson, Bieber, Selena after premier of her movie

Hollywood celebrities Robert Pattinson, Justin Bieber and Selena Gomez, who came to encourage pop sensation Katy Perry at the premier of her autobiographical 3D movie, Katy Perry: Part of Me, were seen partying together whole night on Tuesday. After attending the screening of the film, the stars first went to the infamous Chateau Marmont hotel with Katy and then they left for the opening ceremony of David Arquette's new nightclub, Bootsy Bellows, in Justin's $200,000 Mercedes Benz minivan. It was reported that the teenage couple, Justin and Selena, enjoyed the evening out with Hollywood heartthrob Robert and singer Katy but the Twilight stars girlfriend Kristen Stewart was missing from the scene as she is currently in Paris to promote her upcoming movie Snow White and the Huntsman. According to a source, ''Rob and Katy are good friends so he was happy to celebrate with her, it wasn't just the four of them, but everyone was close.'' The source told UsMagazine.com that Robert has been keeping in touch with Katy since her divorce from Russell Brand last December but they are just friends. ''He's just checking in on her. It's not romantic at all. They're friends,'' the source added.