A teenager who died suddenly in his sleep last Sunday had no known previous medical history which could explain the tragedy.

William Pfeiffer, 14, is being remembered as a happy boy with a bright smile and a heart of gold by his parents, five siblings, grandparents and school friends.

The South Australian boy spent his last hours at his grandparents' Adelaide home, laughing and enjoying their company.

'No parent should ever have to endure the loss of a child,' family friend Nicole Baans wrote on the fundraiser she has set up for William's distraught family.

William Pfeiffer (pictured), 14, who died suddenly in his sleep last Sunday had no known previous medical history which could explain the tragedy

'I am reaching out to those who knew and loved William and his family in the hope that we can band together to ease the financial burden,' she wrote.

'As far as we know, he was a perfectly fit and healthy 14-year-old, (there) was nothing wrong with him,' Ms Baans told Yahoo News.

She said William's mum Karen Lynch and stepdad Mike Shaw hope an autopsy will explain what happened to their boy, who was known for wearing bright socks.

Ms Banns said William was a 'caring' and 'sensitive' boy and that such attributes runs in the family.

William's (picture) mum Karen Lynch and stepdad Mike Shaw hope an autopsy will explain what happened to their boy, who was known for wearing bright socks

His mum is a photographer for Heartfelt, a volunteer organisation which takes photos for families who have experienced stillbirth or who have children with life-threatening illnesses.

'She's such a giving person for other families in their time of need. So it's just so sad that she now has to feel this pain herself,' the family friend said.

William's school at Golden Grove in Adelaide's outer north-east is planning a memorial for him, with all students invited to wear colourful socks on the day.