Family and friends remember 'Partridge Family' star David Cassidy

Cassidy starred in the 1970s sitcom "The Partridge Family."

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.

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