An intensive foot search of the area surrounding the remote homestead where Gus Lamont vanished has been called off after no trace of the four-year-old was found.
South Australian police announced on Friday the renewed four-day search at Oak Park Station had concluded without any evidence being located.
In the 20 days since he disappeared, only a single footprint with a "very similar boot pattern" to Gus's footwear has been found.
Trackers, local property owners and searchers from SA Police, the Defence Force and State Emergency Service this week focused on a 5.5km radius around the homestead, which equated to a search area of 95 sq km.
"Police had been hopeful the extensive ground searches would uncover any evidence of Gus, but this has not been the case," SAPOL said in a statement.
Extensive resources including Polair, drones, and infrared and satellite technology were used to support more than 100 ground searchers.
"Police have been making every effort to return Gus to his family through detailed, meticulous and protracted searching of the property and this remains a priority," police said.
Taskforce Horizon was set up this week to investigate the disappearance of Gus, who was last seen at the station homestead by his grandmother at 5pm on September 27.
The search at the property, about 40km south of Yunta, in SA's Mid North region, had been one of the largest ever undertaken by SA Police, and the initial area covered an estimated 470 sq km.
Temperatures in the mid-thirties, dust and difficult terrain had added to the challenges facing searchers.
The Lamont family had continued to co-operate fully with investigators and were being supported by a victim contact officer, police said.
"The search has been reviewed by senior officers not involved in the operation and subject to constant reviews to ensure completeness," they said.
As the search concluded, the mother of murdered Queensland teenager Phoebe Bishop sent a message of support to the Lamont family.
"In the hope that Gus's family sees this. My advice is that to protect your own mental health and ability to function. Stay off social media and the news. Keep looking and keeping your hopes alive," Kylie Johnson wrote in a letter shared on social media.
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