Olsen turns out for a rockin' rooftop party in New York City. Plus: Gwen Stefani, Prince Harry, Shannen Doherty and more

PRACTICE MAKES PERFECT

Rihanna is all business in her blazer-and-miniskirt ensemble as she heads into New York's Radio City Music Hall Thursday to rehearse for the 5th annual Fashion Rocks concert, airing Sept. 9 on CBS.