Buzz News Roundup, 3/19

• TV Guide reports that Michelle Trachtenberg will head to Gossip Girl to play a nemesis from Serena's past.
• The Sci-Fi Channel has signed Rosario Dawson to develop True Believer, the pilot for a proposed series based on a comic book she co-created, Variety reports.
• Billboard reports that the Dave Matthews Band and Tom Petty & the Heartbreakers will headline the first Mile High Music Festival in July in Commerce City, Colorado.
• ComingSoon reports on the all-star cast — including Gerard Butler, America Ferrera and Jonah Hill, among others — set to provide voices for the 3-D animated movie How to Train Your Dragon.
• Anton Yelchin will play Kyle Reese in the next Terminator movie, writes The Hollywood Reporter.
• Ellen DeGeneres will return for a second year as host of Idol Gives Back, Broadcasting & Cable reports.
• Snoop Dogg's latest album had his lowest first-week sales total ever, finishing at No. 3 on the charts and being beaten by Miami rapper Rick Ross and a NOW compilation, Billboard reports.
• The Hollywood Reporter has news on the cast set up so far for the gay wedding comedy For Better or for Worse, which includes Janeane Garofalo, Rebecca Gayheart and new mom Soleil Moon Frye.
• 3:10 to Yuma director James Mangold will helm a Cyclops movie, ComingSoon reports.