Celebrities got into character this week, as they clocked time on their current projects. Zac Efron dressed up like a bike messenger on the New York set of New Year's Eve, while Lady Gaga put on a costume as . . . herself. Check them out, plus the rest of this week's stars on the set, including Ryan Reynolds, Sarah Jessica Parker, the cast of Gossip Girl, and more!
Zac Efron, Lady Gaga, Ryan Reynolds, and More in Stars on the Set This Week!