Lee Kirkham, 50, has been missing since January 4.
“I’m here today to appeal to people to come forward if they have any information about my son Lee,” Mr Kirkham’s father, Michael Kirkham, said before breaking down in tears.
The father-of-one was last seen at the Mandurah Forum Shopping Centre and then later at night on the street where he lived in Barragup.
“We hold grave concerns for his health and safety and his 10-year-old son is worried about his dad,” Inspector Peter Morrissey from the Mandurah District Office said.
“We do not believe Lee is in possession of a mobile phone, a wallet, or a vehicle.”
Police said they believed he could be carrying cash.
A bush search of semi-rural Barragup has been conducted, which involved mounted police, drones, and the air wing.
Water police have also combed the 280-hectare piece of land that Mr Kirkham’s home backs onto.
But so far, all searches have been unsuccessful.
Michael said that if his son was watching, he wants him to get in contact as soon as possible.