"She was an incredible person and I will always remember the years we spent together fondly," Ashmore shared of Trachtenberg

The actress played socialite Georgina Sparks on the hit CW series

Trachtenberg played Georgina Sparks in both the original series and the 2021 reboot

On Feb. 26, PEOPLE confirmed the late actress' sudden death at age 39

The 'Buffy the Vampire Slayer' and 'Gossip Girl' alum has died at age 39

The NYPD confirmed to PEOPLE that Trachtenberg was found "unconscious and unresponsive" in her Manhattan apartment on Wednesday, Feb. 26 and pronounced dead at the scene

The actress, known for her roles in 'Buffy the Vampire Slayer,' 'EuroTrip' and 'Gossip Girl,' died at age 39 on Feb. 26, 2025

She starred on the cult-beloved TV series as Buffy's younger sister Dawn, and was also featured on Gossip Girl and the movie EuroTrip.

In her final Instagram post — shared a week before she was found dead — the star said she "wanted to look like naughty #tinkerbell"

The 'Gossip Girl' actress was found dead on Feb. 26 at age 39

"I wish I could have helped," O'Donnell said of Trachtenberg, who died at 39 years old

Michelle Trachtenberg was linked to her boyfriend, Jay Cohen, in 2020, five years before her death on Feb. 26

The actress has died at age 39