Michelle Trachtenberg’s Gossip Girl costars, Ed Westwick and Chace Crawford, are paying tribute to her after her sudden death at age 39.

Trachtenberg — who played socialite Georgina Sparks on the hit CW series — was found dead on Wednesday, Feb. 26 in a New York City apartment near Columbus Circle. The investigation is ongoing, although police say "criminality is not suspected."

The actress first appeared on the series in season 1’s "Desperately Seeking Serena" and ultimately starred in 28 episodes total. She reprised her character in two episodes of the 2021 reboot of the same name. 

In the wake of the news, Westwick, 37, who played Chuck Bass for the show's original run from 2007 to 2012, paid tribute to Trachtenberg in a statement shared with PEOPLE.

“‘It’s been a long time since I’ve seen Michelle but I remember a talented, sharp, funny and warm soul,” he shared. “Thinking of her and the family. So sad.’”

He also remembered his late costar in an emotional post on his Instagram Stories.

Sharing a photo of her character, he wrote, "So sad to hear of the passing of @michelletrachtenberg. Sending prayers," along with a prayer hands and white heart emoji.

Show creators Josh Schwartz and Stephanie Savage are also grieving Trachtenberg. In a joint statement to PEOPLE, they said, "We are deeply saddened by the news of Michelle’s passing. Michelle was so funny, kind, and talented."

The two added, "Her portrayal of Georgina Sparks was an iconic fan favorite, and grew from a one season villain to a beloved character who returned over the course of six seasons. She was a delight to have on set and will be deeply missed. Our thoughts are with her family."

Chace Crawford, who played Nate Archibald on Gossip Girl, paid tribute to his late costar on Instagram.

"Michelle was one of a kind," the actor, 39, shared in the post. "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 ❤️"

His tribute included three candid photos with Trachtenberg, including two close-up selfies and another behind-the-scenes pic where he sported a fake baby bump.

Taylor Momsen, who played Jenny Humphrey, was "in shock" over Tractenberg's death, whom she described as "smart and sassy, bold and sensitive, funny as f--- and filled with fire."

"I am so grateful to have had a friend like you in my life for so long..You were a true friend to me which is a rarity in this world and I can’t believe I won’t hear your voice again," Momsen added in her Instagram tribute. "I grieve with all her fans around the world, and my heart is with her family and loved ones."

The TV star additionally starred in the seminal drama series Buffy the Vampire Slayer as Dawn Summers. Several of her former colleagues have shared tributes in her honor, including James Marsters and David Boreanaz.

Marsters, who played Spike on the show, said in statement to 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."

Boreanaz — who played the vampire Angel — also reacted to her death, writing on his Instagram Story, “So very sad …horrible news. RIP and prayers to her and her family.”

In addition to Gossip Girl and Buffy, Trachtenberg starred in Harriet the Spy, Eurotrip, Ice Princess and 17 Again.

The actress's cause of death has yet to be revealed. However, a source told ABC News that she had recently undergone a liver transplant and may have experienced complications.

Trachtenberg never publicly shared any health conditions, but she shut down critics in January 2024 who made comments about her appearance after she shared a selfie on Instagram. "Fun fact. This is my face," she wrote. "Not malnutrition no problems. Why do you have to hate? Get a calendar."

In another post, the actress wrote, "I’ve received several comments recently about my appearance. I have never had plastic surgery I am happy and healthy. Check yourself haters."