Leighton Meester gossip girls

gossip girls Michelle Trachtenberg dress gossip girl

Monday night, Gossip Girl Leighton Meester sang at the Troubadour in West Hollywood and co-star Michelle Trachtenberg stopped by to enjoy the show ... and hopefully not gossip about it.

Leighton is working to cultivate herself as a double threat -- she sang in the flick Country Strong and has collaborated on tracks with other artists.

The two were all smiles -- Leighton was especially bashful in front of the cameras as a mystery man tried to hide her face. Check out the pics in our gallery below and our video after the jump!