Police and State Emergency Service volunteers are searching for a 46-year-old man missing in densely wooded ironstone country in the Goldfields.
Michael Keith Graham was last seen at 10pm on Sunday while camping with friend Peter Holloway 70km north-east of Menzies.
When Mr Holloway woke the next morning, Mr Graham was not there. It is believed he wandered away from the camp during the night.
Sgt Mark Mariott said Mr Graham had not left a note saying where he was going and he had no water or navigation equipment with him.
Police are searching a 100sqkm region of undulating hills crossed with dry creek beds.
About 20 SES volunteers from Kalgoorlie, Norseman, Leonora, Laverton, Menzies and Perth have joined the search.
Department of Fire and Emergency Services liaison officer Colin Brown said sniffer dogs may also be used to track the missing man.
Sgt Mariott said a helicopter pilot contracted by the police took part in the search yesterday and six police horses were due to arrive from Perth this morning.
It is understood Mr Graham arrived in Menzies from the Eastern States earlier this month and the two men had been prospecting for gold.