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

TOUGH CALL

After a few good laughs in Beverly Hills, it's down to business for Lindsay Lohan, who gives a close inspection of a potential purchase Thursday while shopping at L.A. boutique Satine with girlfriend Samantha Ronson (not pictured).