Michelle Trachtenberg, the actress known for roles in series including Buffy the Vampire Slayer and Gossip Girl, has died, according to US media outlets. She was 39 years old.

Police said officers responded to an emergency call just after 8:00 am local time last Wednesday, The New York Times said, where they found her in her Manhattan apartment unconscious and unresponsive. Emergency medical workers pronounced her dead without giving a cause. Police said foul play was not suspected. Citing anonymous sources, ABC News reported that the actress recently underwent a liver transplant, and was perhaps experiencing complications.

Condolences poured in from Trachtenberg’s co-stars, including Gossip Girl actors Blake Lively, Taylor Momsen and Ed Westwick. Momsen, in an Instagram post, said she was “in shock” over Trachtenberg’s passing.

David Boreanaz, her Buffy the Vampire Slayer co-star shared, “So very sad… horrible news. RIP and prayers to her and her family.” Kim Cattrall, who was in Ice Princess with the late actress, took to X and said the news was heartbreaking, “So talented, much too young. RIP sweet beauty.”