A member of the search party looking for missing four-year-old Gus Lamont has revealed there is zero evidence he is on the property he vanished from.

The multi-agency search has now been abandoned with the case handed back to police after soldiers, volunteers and officers spent nine days scouring both land and water on the sheep farm near Yunta in rural SA where Gus disappeared on September 27.

A former SES volunteer, Jason O’Connell, who joined the search and helped walk the 60sqkm property with the missing boy’s father, has now spoken out about the bizarre theories around the case.

“My heart breaks for (the father),” O’Connell told 7NEWS.

“It’s been searched. (Gus) is not there.”

O’Connell was given police approval to use his tracking skills to help with the search.

He told 7NEWS that he has never seen a case like this before, where there has been not been a single trace of the person who has gone missing.

“I just don’t get how (Gus) vanished like that,” O’Connell said.

Gus was last seen playing on a mound of dirt outside his grandmother’s homestead about 5pm on the day he went missing.

His grandmother said she went to call him inside 30 minutes later, but he was gone.

“According to a family member, he is a shy but adventurous child. While a good walker, he has never left the family property previously,” SA Police Assistant Commissioner Ian Parrott said.

Wild theories about what has happened to Gus have been circulating on social media, and O’Connell said they were causing emotional distress for Gus’ father.

“Wedgetail (eagles) will pick up 1kg or two, they’re not going to pick up a four-year-old,” O’Connell said.

“There’s no pigs, there’s no wild dogs, there’s no foxes.”

The search shifted to a recovery operation last week, after his family were warned by senior police that “Gus may not have survived due to the passage of time, his age and the nature of the terrain he is missing in,” Parrott said.

“We are confident that we have done all we can to locate Gus within the search area.”

There were 30 SES volunteers sent to the property each day of the search, with the Australian Defence Force also providing 50 personnel for two days of the search, as hopes of finding the boy alive there slowly dwindled.

Police will now re-examine all evidence they have gathered on the case, as part of the ongoing investigation.

“He’s a little tacker, you don’t want to leave him out there,” O’Connell said.

—With reporting from Hannah Foord