Former child star Erin Moran who played Joanie Cunningham in the US sitcom "Happy Days" has been found dead at 56.

Henry Winkler has led tributes to his former co-star by tweeting "Erin, now you will finally have the peace you wanted so badly here on earth, Rest in it serenely now, too soon."

Director and former co-star to Erin, Ron Howard also paid tribute to his on-screen sister saying "such sad sad news. RIP Erin. I'll always choose to remember you on our show making scenes better, getting laughs and lighting up TV screens."

Police received a 911 call on Saturday after Erin had been found unresponsive in Indiana.

The cause of Erin's death is currently unknown.

Erin became a household name when she joined the show Happy Days at just 13 years old where she played Ron Howard's sister Joanie for almost a decade.

She would later appear with Scott Baio in the "Happy Days" spinoff "Joanie Loves Chachi."

The show only ran for one season and Erin returned to 'Happy Days' for its 11th and final season in 1983.

The actress went on to make smaller television appearances on various series including Murder, She Wrote and The Love Boat.

The later years in the star's life were reportedly plagued by hardship with reports in 2012 that Erin was homeless and living in hotels after being kicked out of her mother-in-law's mobile home.