Kendra Wilkinson and Bridget Marquardt, two of the three stars of "Girls Next Door," the E! reality show that focused on Hefner's girlfriends from 2005 until 2010, expressed their sentiments in an Instagram post.
"So sad but forever grateful for all the wonderful memories and amazing experiences," Marquardt wrote.
Added Wilkinson: "Can't really put in to words how I really feel. It's easy to say he will be missed and how much I loved him. There's a lot more than that."
Pamela Anderson, who appeared on the cover of Playboy 14 times, shared a video on Instagram that featured her crying as she said a final goodbye to the magazine publisher.
"I am me because of you. You taught me everything important about freedom and respect. Outside of my family, you were the most important person in my life. You gave me my life," she wrote in a lengthy caption. "I'm in such deep shock. But you were old, your back hurt you so much. Last time I saw you, you were using a walker. You didn't want me to see. You couldn't hear. You had a piece of paper in your pocket you showed me - with my name Pamela with a heart around it.
"Thank you for making the world a better place. A freeer and sexier place," she continued. "You were a gentleman: charming, elegant, chivalrous and so much fun."
Other celebrities who spoke out about Hefner included:
Actress and former Playmate Jenny McCarthy
Actress and former Playmate Donna D'Errico
Hall of Fame sports announcer Michael Buffer
Reality TV star Kim Kardashian West
Comedian Richard Lewis
Musician Gene Simmons
Model and reality TV star Adrianne Curry
Reality TV star Heidi Montag
Singer Aubrey O'Day
Actor Rob Lowe
Civil rights activist the Rev. Jesse Jackson Sr.
Singer and actress Nancy Sinatra
Actor Mark Hamill
"Live! With Kelly" co-host Ryan Seacrest
Reality TV star Paris Hilton