Leighton MeesterAs individuals from across the globe come together for World AIDS Day 2009, ONE is launching "Coming Together as ONE" -- a new PSA campaign designed to mobilize young people to get involved in the fight against extreme poverty and preventable disease. Leighton Meester, Ed Westwick, Hayden Panettiere and Ashley Greene are among the many stars who are raising support for the campaign. Watch the new PSA: