Matthew Perry's family have said they are "heartbroken" by his death, adding he "brought so much joy to the world".
Perry, 54, best known for his role as Chandler Bing, was found unresponsive in a jacuzzi at his Los Angeles home at around 4pm on Saturday, the LA Times and TMZ reports.
Speaking to People magazine, his family said: "We are heartbroken by the tragic loss of our beloved son and brother. Matthew brought so much joy to the world, both as an actor and a friend."
Members of the Friends cast and crew have also been among those to pay tribute.
The series' co-creators Marta Kauffman and David Crane and its executive producer Kevin Bright said they were "shocked and deeply, deeply saddened".
"It still seems impossible. All we can say is that we feel blessed to have had him as part of our lives," they wrote in a statement.
"He was a brilliant talent. It's a cliche to say that an actor makes a role their own, but in Matthew's case, there are no truer words.
"From the day we first heard him embody the role of Chandler Bing, there was no one else for us."
Describing him as "always the funniest person in the room", they said he was also the "sweetest, with a giving, selfless heart".
"We send all of our love to his family and friends. This truly is The One Where Our Hearts Are Broken."
Maggie Wheeler, who played Perry's on-screen girlfriend Janice, wrote on Instagram: "What a loss. The world will miss you, Matthew Perry."
Perry struggled with drug and alcohol addiction and was in and out of rehab while filming the hit show.
Hank Azaria, who played David in Friends, posted on Instagram that the pair were like "brothers".
"Matthew was the first friend I made in Los Angeles when I moved there. I was 21 he was 16," he said in a video.
"We were there for each other in the early days of our career and he was to me, as funny as he was on Friends and he was and other things too, in person he was just the funniest man ever."
Speaking of his addiction issues, he added: "I really loved him. A lot of us who were close to him felt like we lost him to drugs and alcohol a long time ago because as he documented in his autobiography there was so much suffering.
"I had to pick it up and put down the biography like 11 times it was so painful for me to read."
Duchess of York Sarah Ferguson also left her memories of meeting Perry, sharing the time she worked with him on an episode of Friends.
She wrote on social media: "I remember being thrilled to have met a natural talent, comedian and brilliant actor.
"It is a tragedy to lose you so early in life, rest in peace dear Matthew... you have given so much joy and laughter to so many."
Morgan Fairchild, who played Chandler's mother, wrote on X: "The loss of such a brilliant young actor is a shock."
She offered his condolences to his friends and family, "especially his dad", whom she had also worked with.
American actor Paget Brewster, who played Kathy in Friends, who dated Perry's and his co-star Matt LeBlanc's character Joey, also posted about him on X.
"I'm so very sad to hear about @MatthewPerry," she wrote. "He was lovely to me on Friends and every time I saw him in the decades after."
Commenting on his struggle with addiction, she added: "Please read his book. It was his legacy to help."
Canadian PM 'played schoolyard games' with star
Canadian Prime Minister Justin Trudeau, who went to school with Perry, described his death as "shocking and saddening".
"I'll never forget the schoolyard games we used to play, and I know people around the world are never going to forget the joy he brought them," he said in a post on X.
"Thanks for all the laughs, Matthew. You were loved - and you will be missed."
Appearing on the Jimmy Kimmel show Perry had previously admitted to "beating up" the politician in the playground.
Actor Gwyneth Paltrow knew Perry from when he was in his 20s - just before the Friends pilot aired. Writing on Instagram she recalled a "magical summer" they spent together.
"He was so funny and so sweet and so much fun to be with. We drove out to swim in creeks, had beers in the local college bar, kissed in a field of long grass. It was a magical summer," she posted.
Actor Selma Blair was another friend to pay her respects.
She said: "My oldest boyfriend. All of us loved Matthew Perry, and I did especially. Every day. I loved him unconditionally. And he me."
Perry's hockey team plays theme tune before game
A lifelong ice hockey fan, Perry's team the LA Kings paid tribute to him by playing the Friends theme tune before their game against the Vegas Golden Knights on Saturday.
Teary fans were also seen laying flowers outside the famous 'Friends apartment' in Greenwich Village, New York.
Among the other famous faces to pay their respects were Adele, actor Viola Davis and Bruce Willis's daughter Rumer, who worked with Perry on The Whole Nine Yards.
The Friends star's death is not being treated as suspicious.
There is no confirmed cause of death but police are investigating.