The actress played socialite Georgina Sparks on the hit CW series Michelle Trachtenberg’s Gossip Girl costars, Ed Westwick and Chace Crawford, are paying tribute to her after her sudden death at age 39.

Blake Lively, David Boreanaz, Ed Westwick, Kim Cattrall, Kenan Thompson, Melissa Joan Hart and more shared tributes to Trachtenberg.

Trachtenberg began her career as a child star in the 1996 movie Harriet the Spy, which also starred Rosie O’Donnell and Eartha Kitt. She went on to join the cast of Buffy the Vampire Slayer as Sarah Michelle Gellar ’s sister, Dawn.