By Leah Abrahams
Updated Nov 21, 2011 @ 1:05 pm
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Credit: Dennis Van Tine/ABACAUSA.com

Blake Lively (in Marchesa) and Chloe Moretz (in Stella McCartney) joined Leighton Meester, Michelle Tractenberg, and more to celebrate Gossip Girl's 100th episodeat Cipriani Wall Street in New York City. Click through the gallery to see Emma Watson, Taylor Swift and more stars at the weekend's hottest parties!