Michelle Trachtenberg, an actress best known for her roles in “Buffy the Vampire Slayer” and “Gossip Girl,” has died at age 39.

Trachtenberg was found dead Wednesday in her New York City apartment near Columbus Circle just after 8 a.m. local time by her mother, police sources told ABC News.

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The sources told ABC News the actress recently underwent a liver transplant and may have been experiencing complications. Trachtenberg is believed to have died of natural causes and no foul play is suspected.

An autopsy will be conducted by the medical examiner’s office to determine the cause and manner of death.

Trachtenberg, a New York City native, made her acting debut as a child star with roles in Nickelodeon projects, including the television series “The Adventure of Pete & Pete” and the film “Harriet the Spy.”

Her big break came when she was cast on “Buffy the Vampire Slayer” as Dawn, the younger sister of Sarah Michelle Gellar’s titular character, from 2000 to 2003. The role earned her a Teen Choice Award nomination for choice TV sidekick in 2001.

Trachtenberg recently reminisced on her days co-starring with Gellar on “Buffy.” Just last month, she shared a photo of them together, captioning it: “Slay all day! Always loved this twinning photo of us! #buffy #dawn #sister #womancrushwednesday.”

The actress also made a cameo in Fall Out Boy’s music video for the band’s hit song “This Ain’t a Scene, It’s an Arms Race” in 2007.

Trachtenberg starred as Georgina Sparks on “Gossip Girl” from 2008 to 2012. For her role, she was nominated as the choice TV villain at the Teen Choice Award in 2012.