Michelle Trachtenberg, a former child star who appeared in the 1996 “Harriet the Spy” hit movie and went on to co-star in two buzzy millennial-era TV shows — “Buffy the Vampire Slayer” and “Gossip Girl” — has died. She was 39.

Police responded to a 911 call shortly after 8am at a 51-story luxury apartment tower in Manhattan’s Hell’s Kitchen neighbourhood where officers found Trachtenberg "unconscious and unresponsive,” according to an NYPD statement.

Paramedics pronounced her dead at the scene.

No foul play was suspected and the New York Medical Examiner is investigating the cause of death, police said.

“The family requests privacy for their loss," Trachtenberg's representative, Gary Mantoosh, said in a statement on Wednesday.

Trachtenberg was eight when she began playing Nona Mecklenberg on Nickelodeon’s “The Adventures of Pete & Pete” from 1994 to 1996 and then starred in the title role in the film adaptations of “Harriet the Spy” and “Inspector Gadget,” opposite Matthew Broderick.

“Michelle comes off as genuine because she really is a genuine kid. Everyone can identify with her,” said Debby Beece, president of Nickelodeon Movies in 1996.

In 2000 Trachtenberg joined the cast of “Buffy,” playing Dawn Summers, the younger sister of the title character played by Sarah Michelle Gellar between 2000 and 2003. (AP)