New York, New York - Harriet the Spy star Michelle Trachtenberg has suddenly died at the age of 39.

On Tuesday, ABC News confirmed that Trachtenberg was found dead in a New York City apartment near Columbus Circle.

The New York Post further reported that the Nickelodeon actor was found by her mother around 8 AM in a 51-story luxury apartment complex and had recently undergone a liver transplant.

The NYPD shared Trachtenberg was found "unconscious and unresponsive" by police and pronounced dead by EMS workers.

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Authorities have shared that "her death is not being investigated as suspicious."

The Eurotrip star's unexpected death comes after concerning Instagram posts where she appeared to look gaunt and frail.

Last January, Trachtenberg dismissed fans' concerns by saying that she was "happy and healthy" and did not get plastic surgery.

Trachtenberg was best known for her breakout performance as Harriet Walsh in the 1996 Nickelodeon movie also starring Rosie O'Donnell, as well as her TV roles as Dawn Summers on Buffy the Vampire Slayer and Georgina Sparks on Gossip Girl.