Parties Mary Kate and AshleyKevin Mazur/Getty Images

Mary-Kate and Ashley Olsen partied to support JCPenney and the retailer’s grand new plans—like slashing prices by 40% and new designer collaborations—at Pier 57 in New York City. The twins design a juniors line for the store named Olsenboye. Click through the gallery to see Kate Beckinsale, Drew Barrymore, and more stars at last night’s hottest parties!