The parents of missing four-year-old Gus Lamont say their “lives have been shattered” as they appeal to the public for any information that could help find him.

Gus – also known as Angus – went missing from his family’s sheep station in outback South Australia on 27 September last year.

South Australian police initially believed he had wandered off, but after multiple extensive searches, police announced on 5 February that the case was now considered a major crime, and that they had identified an alleged suspect.

Police said the suspect was someone who lived with Gus at Oak Park station although they emphasised it was not one of his parents.

In a statement on Tuesday, Gus’s parents Josh and Jess released another photograph of Gus and a short video of him on a bike.

“We are united in our grief, and we are united in our search for answers about what happened to our little boy, Gus, who means everything to us,” they said in a statement issued by SA police.

“Our lives have been shattered, and every moment without him is unbearable.

“We know someone out there may have information. If someone knows what happened, we are pleading with that person – or anyone who may have seen or heard anything – to please come forward.

“Even the smallest detail could give us the answers we so desperately need.”

They also thanked everyone who had been involved in the search, and “the friends, family and supporters who have shown such compassion, concern and assistance during this heartbreaking time”.

“Your kindness has helped carry us through the darkest days of our lives.

“All we want is to bring Gus home and understand what happened to our beautiful boy.”

Oak Park station is near Yunta, about 300km inland from Adelaide.

Gus was playing outside at 5pm on 27 September. When his grandmother went to call him inside half an hour later he was gone, police were told.

He was wearing a blue T-shirt with a yellow Minion on the front, a grey sun hat over his blond curls, light-grey pants and boots.

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Drones, divers and dogs joined teams of volunteers, police, emergency services and defence force personnel to search the 60,000-hectare property. As the search went on, hope of finding Gus alive dwindled, and in early October police prepared the family for the news that he may not have survived.

Police have said throughout that there was no evidence of foul play but that nothing could be ruled out and that the family was cooperating.

But on 5 February, Det Supt Darren Fielke, the officer in charge of major crime, said police now thought it unlikely Gus had wandered off or that he had been abducted.

He said police had “identified a number of inconsistencies and discrepancies” in the information they had been given and that one person who lives at Oak Park station was no longer cooperating and was considered a suspect.

Police had seized a vehicle, a motorbike and electronic devices from the property.

Gus’s two grandmothers released a joint statement via their lawyers saying the family has “cooperated fully with the investigation and want nothing more than to find Gus and reunite him with his mum and dad”.

On 16 February, police arrested a 75-year-old on unrelated firearm offences, and said the charges stemmed from a previous search at Oak Park station but were not related to Gus’s disappearance.

At that point, detectives from Taskforce Horizon returned to the property to continue searching for more evidence but did not uncover anything. The investigation is ongoing.

Fielke said the police would “continue to thoroughly and meticulously investigate the disappearance of Gus until we get an outcome”.

Anyone with information should contact Crime Stoppers on 1800 333 000.