Michelle Trachtenberg, who appeared in the television series Buffy the Vampire Slayer and Gossip Girl, has died. She was 39.

“It is with great sadness to confirm that Michelle Trachtenberg has passed away,” the actress’s publicist Gary Mantoosh told Yahoo Entertainment. “The family requests privacy for their loss. There are no further details at this time.”

Trachtenberg was found dead in her New York City apartment on Feb. 26. A spokesperson for the NYPD told Yahoo that police responded to a 911 call at the high-rise building at 8:01 a.m.

“Upon arrival, officers observed a 39-year-old female unconscious and unresponsive,” the spokesperson said. “EMS responded to the location and pronounced the victim deceased.”

Trachtenberg’s death is not believed to be suspicious, police said. An autopsy will be conducted to determine the cause of death, and an investigation is ongoing.

Michelle Trachtenberg at an event in Los Angeles, Nov. 2, 2023. (Gilbert Flores/WWD via Getty Images)

ABC News reported that Trachtenberg’s mother discovered her in the apartment. The outlet said that Trachtenberg had recently undergone a liver transplant and that it is possible there were complications.

Trachtenberg shared an Instagram post as recently as Feb. 18, with a throwback image.

Born in New York City, Trachtenberg started acting at age 3, and her first major TV role was on Nickelodeon’s The Adventures of Pete & Pete in 1994. She went on to star in the 1996 film Harriet the Spy.

Trachtenberg broke through as a young actor playing the sister of Michelle Gellar’s Buffy the Vampire Slayer from 2000 to 2003. In 2004, she was nominated for a Daytime Emmy for Outstanding Performer in a Children’s Series for her role in Truth or Scare. She later landed the role of Georgina Sparks on the CW’s Gossip Girl, which ran from 2007 to 2012. She appeared in the HBO Max reboot in 2022 and 2023.

Trachtenberg at the Kid’s Choice Awards in 1998. (Jeff Kravitz/FilmMagic)

Her later work also included hosting the Tubi true crime television series Meet, Marry, Murder in 2021.

Many of Trachtenberg’s former co-stars have paid tribute to her after the news broke.

Chace Crawford, who played Nate Archibald on Gossip Girl, honored Trachtenberg in an Instagram post: “Michelle was one of a kind. I remember her coming on set for the first time and just absolutely owning it. She was a force of nature and just so so unapologetically funny and magnetic.. remembering those years with a big smile. Just a terrible loss. Love you”

Alyson Hannigan, who played Willow Rosenberg on Buffy the Vampire Slayer, wrote in an Instagram post, “I am deeply saddened by the news of Michelle’s passing. She brought a loving energy to the set of Buffy. My thoughts are with Michelle’s family and friends.”

Emma Caulfield, who played Anya on Buffy the Vampire Slayer, posted a tribute to Trachtenberg on her Instagram Stories, writing, “I’m so sorry your bright light died so young. Our Buffy family lost a little sister today … Rest in peace lovely Mish Mish. You were loved.”

(Emma Caulfield via Instagram)

Clare Kramer, who played Glory on Buffy the Vampire Slayer, wrote in an Instagram post, “Peace out little one. A talented & kind soul gone way too soon! You’re free to fly now…”

Gossip Girl‘s Ed Westwick, who played Chuck Bass, wrote on Instagram Stories, “So sad to hear of the passing of @michelletrachtenberg sending prayers.”

(Ed Westwick via Instagram)

David Boreanaz, who played Angel on Buffy, wrote on Instagram Stories, “So very sad …horrible news. RIP and prayers to her and her family.”

(David Boreanaz via Instagram)

Buffy’s James Marsters, who played Spike, told People, “My heart is heavy today. We have lost a beautiful soul. Michelle was fiercely intelligent, howlingly funny and a very talented person. She died much too young, and leaves behind scores of people who knew and loved her.”

(James Marsters via Instagram)

Rosie O’Donnell, who co-starred in Harriet the Spy, called the news “heartbreaking” in a statement to the same outlet. “I loved her very much. She struggled the last few years. I wish I could have helped.”

Rosie O’Donnell and Trachtenberg at the New York City premiere of Harriet the Spy, July 9, 1996. (Evan Agostini/Liaison)

Kim Cattrall, who appeared in Ice Princess (2005) with Trachtenberg, also called the loss “heartbreaking” in a post on X. “So talented, much too young. RIP Sweet Beauty.”

She later shared a photo of them from their movie on Instagram.

Melissa Gilbert, who played Trachtenberg’s mother in the 1996 TV movie A Holiday for Love, wrote on Instagram, “Oh Michy…and we lived so close to one another…..my heart aches for your family and all those who loved you so.”

Kenan Thompson, a fellow former Nickelodeon child star, posted a video of a sketch they did at the 1999 Nickelodeon Kids’ Choice Awards, and wrote: “Our first Nick movie star has departed us!! She was my friend and now she rests!! 🙏🏾 Check on your people!!!”

Additional reporting by Neia Balao.

Correction: A previous version of this story misstated Trachtenberg’s age when she acted on The Adventures of Pete & Pete.