With her pooch in tow, the Gossip Girl star celebrates her 21st b-day on the New York City set of her show. Plus: Ashlee Simpson, Lindsay Lohan, Paris Hilton and more

ON A STROLL

Tom Cruise joins Katie Holmes and daughter Suri, 2, for a family tour around New York on Friday. The mother-daughter pair are no stranger to the Big Apple sites: They've been spotted at playgrounds all over the city while Holmes is in town rehearsing for her Broadway debut.