The actor Michelle Trachtenberg, known for Buffy the Vampire Slayer and Harriet the Spy, has died at the age of 39.

Police sources confirmed her death to both ABC News and the New York Post. There is no cause of death yet known and it has been reported that it is not being investigated as suspicious. She had recently undergone a liver transplant, according to sources.

ABC reports that the actor’s mother found her at a New York apartment.

Trachtenberg was a child actor who started her career at the age of three in commercials before featuring in the Nickelodeon show The Adventures of Pete & Pete and the soap opera All My Children.

She later scored her first lead film role in the comedy adventure Harriet the Spy alongside Rosie O’Donnell. Trachtenberg later said the shoot began on her 10th birthday. “There was a lot required of me,” she said in 2021. “I’m extremely grateful for the experience.”

O’Donnell released a statement following her death. “Heartbreaking,” she said. “I loved her very much. She struggled the last few years. I wish I could have helped.”

Trachtenberg followed the film with a role in Inspector Gadget next to Matthew Broderick.

A role in Buffy the Vampire Slayer came in 2000 with Trachtenberg cast as Dawn Summers until the show ended three years later.

Later film roles included the teen comedy EuroTrip and Gregg Araki’s acclaimed drama Mysterious Skin. “I’m very proud of that film,” she said. “I was this girl who had done glitzy, PG-themed stuff and here’s Gregg Araki, director of Doom Generation, and we sat down and had a cup of coffee and I said, ‘You’re probably not gonna hire me but this is what I got, this is what I feel. If you’re willing to take the chance, I’m willing to go there with you.’ It was the most exhilarating experience I’ve had as an actress.”

In 2005, she played the lead in Disney drama Ice Princess. She also had a recurring role in HBO’s hit series Six Feet Under.

The next few years saw roles in shows such as House and films such as 2006’s Black Christmas remake before she nabbed the role of Georgina Sparks in the teen drama series Gossip Girl. She later played the character again in 2022’s reboot.

“Georgina is actually my favorite character that I’ve played because she’s such an evil B-I-T-C-H,” she said. “That was fun.”

Her Gossip Girl co-star Ed Westwick paid tribute to her today on Instagram. “So sad to hear of the passing of Michelle Trachtenberg,” he wrote. “Sending prayers.”

Trachtenberg’s last big screen role was 2014’s sci-fi thriller The Scribbler, but she does have a project that is yet to be released, a drama called Spyral about mental illness.

Her ex-boyfriend, X-Men star Shawn Ashmore, also paid tribute to her on social media. “Incredibly sad to hear about Michelle’s passing,” he wrote. “She was an incredible person and I will always remember the years we spent together fondly … This is an incredible loss!”