The search for missing four-year-old Gus has entered its seventh day, with no more signs of the boy.

Australian Defence Force personnel and police cadets have joined volunteers and other emergency services workers in the search of South Australia's outback.

The boy was last seen playing in sand on his family's sheep station about 40 kilometres south of Yunta.

Royce Player used to be neighbours with the family and is also an experienced tracker who knows the area well.

"I would've thought they might've found him by now, you never know, this could be something someone's missed somewhere," he said.

"Doesn't take much, and if he's frightened he'll be hiding. Let's hope he's still out there.

"Under a bit of bush, a bloody hole in the ground, or an old motorcar … could be anywhere."

He

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