The pair, along with co-star Taylor Lautner, took to the stage in the Hollywood and Highland Center and sent waiting fans into a frenzy.
Pattinson told the crowd, "First of all, thanks to you guys. Without you, Twilight wouldn't be anywhere, so thanks very much."
And Lautner stunned fans further by announcing: "We have a special treat. The whole entire cast is about ready to come on stage and they're going to answer your questions so thank you, it should be exciting."
The trio was then joined onstage by the rest of the cast, including Kellan Lutz, Nikki Reed and Ashley Greene.
The waiting audience had earlier been entertained by performances by Death Cab For Cutie, Sea Wolf, Anya Marina and Band of Skulls, who all have tracks on the upcoming vampire movie's soundtrack.
The Twilight Mall Tour is continuing across the U.S. over the next two weeks, before wrapping up in New York on 19 November (09).