Leighton Meester and Selena Gomez at Monte Carlo Junket

Leighton Meester and Selena Gomez arrived separately for the Monte Carlo press junket in NYC today, and their costar Katie Cassidy was also on hand at the Ritz Carlton hotel. Selena and Katie already started promoting the project at last week's Monte Carlo premiere, though Leighton couldn't join them on the red carpet since she was busy filming I Hate You, Dad in Boston. The girls did have the support of Andie MacDowell as well as Selena's boyfriend, Justin Bieber, however. It's been a big week for Selena since her album When the Sun Goes Down was released on Tuesday and Monte Carlo hits theaters tomorrow. Leighton has also been juggling her acting and singing careers, and she recently played a sold-out show in LA.