A family statement later confirmed that the entertainer had passed away in hospital, saying: "David died surrounded by those he loved, with joy in his heart and free from the pain that had gripped him for so long".
Cassidy spoke openly about his struggles with alcohol in recent years, after being arrested for drink-driving three times and attending rehab.
Several celebrities, including some of Cassidy's contemporaries, shared memories on Twitter.
Born in 1950 in New York, Cassidy was the son of performers Evelyn Ward and Jack Cassidy, and though he grew up out of the limelight, he ultimately followed in their footsteps. Beau has followed in his parents' footsteps - according to his IMDB bio, he is a singer, songwriter and actor based in NY and Los Angeles. His character, a high school student, was periodically swooned over by young women as he learned to navigate his newfound fame. "Thank you for the abundance and support you have shown him these many years", his publicist told CNN after confirming his death.
The next year, he won the role of Keith Partridge in The Partridge Family, starring opposite his step mother Shirley Jones. "I want to meet my dad", said Wright, who also insists she's not looking for any kind of payout. He posed naked for Rolling Stone in 1972, when he both confided that he had dropped acid as a teenager and smoked pot in front of the magazine's reporter as he watched an episode of The Partridge Family while mocking his own acting.
"I'll feel really good when it's over", he said, adding: "I have an image of myself in five years".
One of Cassidy's fans went on to claim that the actor-singer boasted of a fan club larger than that of Elvis Presley and The Beatles at the height of "Cassidy-mania".
"I'm living on an island", Cassidy said. "And I'm smiling, I'm healthy, I'm a family man".
Cassidy also capitalized on the show's success by cutting a number of solo singles and albums that gave him four more top forty hits including a cover of the Association's "Cherish" (1971 / #9) and the Rascals' "How Can I Be Sure" (1972 / #25).
Corey Feldman said Cassidy inspired him to pursue a career in acting and singing.