Rosie O’Donnell, Gossip Girl and Buffy Costar Tributes

Not long after Trachtenberg’s shocking passing was confirmed, fellow celebrities and former co-stars began paying tribute to the late actress.

Rosie O’Donnell — who starred alongside Trachtenberg in 1996’s Harriet the Spy, which was released when Trachtenberg was just 10 years old and marked her big-screen acting debut — called the news “heartbreaking.”

“I loved her very much. She struggled the last few years. I wish I could have helped,” O’Donnell said in a statement to PEOPLE.

Trachtenberg’s Buffy the Vampire Slayer co-star, Alyson Hannigan took to Instagram to share how “deeply saddened” she is to hear the news of Trachtenberg’s passing. Hannigan recalled her bringing a “loving energy to the set of Buffy.”

David Boreanaz took to his Instagram Story to remember Trachtenberg, writing, “So very sad… horrible news. RIP and prayers to her and her family.

Fellow Buffy co-star James Marsters, who played Spike, shared a tribute as well — writing, “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.”

“My heart goes out to her family who are good people, and are suffering the greatest loss anyone could bear,” he continued. “I hope everyone can give them space to heal in this most difficult time. Godspeed Michelle. You are missed.”

Buffy alum, Emma Caulfield shared a photo of the pair together on her Instagram Story captioning it: “I’m so sorry your bright light died so young. Our Buffy family lost a sister today… Rest in peace lovely Mish Mish. You were loved.”

Ed Westwick — who starred in Gossip Girl alongside the late TV and film star — wrote, “So sad to hear of the passing of @michelletrachtenberg. Sending prayers.”

Fellow GG star Chace Crawford also shared an Instagram tribute, writing, “Michelle was one of a kind. 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 ❤️”

Kim Cattrall, who played Trachtenberg’s coach in Disney’s 2005 film, Ice Princess, also paid tribute to the 39-year-old TV and film star, sharing a photo of the pair form the film on Instagram, writing, “Rest in peace sweet Michelle 💔.”

Melissa Gilbert penned a heartbreaking message for Trachtenberg following the news, sharing a photo from their 1996 film, A Holiday for Love, writing, “Oh Michy … and we lived so close to one another.”

She continued, “My heart aches for your family and all those who loved you so.”

Glee star Chris Colfer shared how “lucky” he felt to be Trachtenberg’s friend.

“Michelle was the absolute sweetest and one of the most supportive people I knew,” he wrote on his Instagram.

Her death was first reported by the New York Post, citing police sources, with those sources telling the news outlet her death is not being investigated as suspicious.

According to TMZ, she recently underwent a liver transplant and police believe she died of natural causes. Per the outlet, police and paramedics responded to a call for a woman in cardiac arrest, and found Michelle unresponsive. She was pronounced dead on the scene.

Perhaps best known to film and television audiences for her work in Gossip Girl, Buffy the Vampire Slayer, and Harriet the Spy, Trachtenberg has largely remained out of the public eye since 2023, but was still active on social media, sharing selfies as recently as two weeks ago.

More celebrity tributes to Trachtenberg continued to roll in Wednesday, including from her fellow Nickelodeon alum, Kenan Thompson, ex Shawn Ashmore and more.

See their moving messages to the late actress below: