Australian Defence Force personnel have joined the search for a four-year-old boy who vanished from his family’s remote sheep station.

On Wednesday, the discovery of a small footprint gave a glimmer of hope as the search missing preschooler Gus on an outback South Australian homestead entered its fifth day.

Searchers have sadly reported that no trace of any other footprints have been found since, which Superintendent Mark Syrus said was “really unusual”.

Early on Thursday, 48 ADF personnel arrived at the search area, about 300 kilometres north of Adelaide. They are expected to help police with ground searches in coming days.

A specialist tracker with deep knowledge of the terrain has been called in to help.

SA Police released a photo of Gus who has been missing for six days. Photo: SA Police

SA Premier Peter Malinauskas said everything would be thrown at the search and his thoughts were with Gus’s family.

“This is a story that has captured everybody’s attention and for good reason,” he told ABC radio on Thursday.

“There is no resource we’re not willing to call on to try and find this beautiful young boy, if we get the chance.”

Four-year-old August, known as Gus, has not been seen since vanishing from his family’s sheep station in SA’s remote mid-north on Saturday afternoon.

With Gus alone in searing temperatures and without food or water since, authorities’ best-case scenario is that he has crawled into shelter and is waiting to be rescued from the property near Yunta.

In a significant development, a footprint was found on Tuesday night, buoying searchers who have worked day and night to bring the preschooler home.

Searchers found a footprint on Tuesday. Photo: SA Police

However, police have also prepared the boy’s family for the worst after five days of searching.

“We’re day six into the search and it’s over 100 hours now since Gus was last seen at the homestead,” Superintendent Mark Syrus told ABC Radio.

“We’ve had a lot of boots on the ground, almost 100 search teams out in the area over the last few days, including a tracker who has been out here for about a day and a half now.

“Unfortunately, in the search yesterday he could not find a trace of any other footprints in the area, which he said was really unusual.”

The lack of evidence has prompted the police to review their search patterns and return to the homestead for a third examination.

Searchers had “a lot of theories” but police remained confident Gus left the area on foot, leading them to focus on a three-kilometre radius from the home, Syrus said.

“We are here to complete the search, and our intention is to find Gus – hopefully alive,” he said.

Gus’s distraught family broke their silence on Tuesday, saying they were “struggling to comprehend what has happened” to him.

“Gus’s absence is felt in all of us, and we miss him more than words can express,” Bill Harbison said on the family’s behalf.

“Our hearts are aching and we are holding on to hope that he will be found and returned safely.”

The adventurous boy had been playing in the sand near the family homestead when he disappeared. Despite frantic efforts stretching for more than three hours, no trace of him was found.

Since then, there have been extensive ground searches involving State Emergency Service volunteers on trail bikes, all-terrain vehicles, dogs and a drone, as well as helicopters, police divers and mounted officers.

Specialist water teams have been called in. Photo: SA Police

Water Operations Police and Mounted Operations Unit joined the search on Monday to search dams and tanks on the property and assist in the ground search.

Police said they were thankful for the support of volunteers and community members.

Gus was wearing a Minions shirt. Photo: SA Police

Gus is Caucasian with long curly, blond hair. He was wearing a grey sun hat, cobalt blue-coloured T-shirt with a yellow Minion on the front, light grey long pants, and boots.

Police don’t believe the disappearance is suspicious.

Anyone with information that could assist the search is urged to contact Crime Stoppers on call 1800 333 000, quoting reference #250513.