 -- David Cassidy died at the age of 67 on Tuesday, and friends and family immediately took to social media to pay their respects to the former "Partridge Family" star.

Cassidy had been hospitalized with organ failure last Wednesday and was in critical condition, his rep told ABC News days before his death.

Jack Cassidy, the nephew of the legendary actor and singer, posted a tribute on Twitter, writing, "In the process of mourning I can't help but thank God for the joy that he brought to countless millions of people! I don't think I'm alone in saying that we will all miss him. God Speed!"

Cassidy starred in the 1970s sitcom "The Partridge Family" as heartthrob Keith Partridge and sold millions of records as the musical group's lead singer.

"Partridge Family" co-star Danny Bonaduce added on Twitter: "I have known, loved, and admired David Cassidy for 48 out of my 58 years. He has been as kind to me as any real brother could ever be. We’ve been through a lot together and he was always there for me. This loss is huge. RIP my dear friend."

Other co-stars, friends and fans shared tributes on Twitter as well.