Ramon Howard John Mahu, known by family and friends as Ray, has not been seen or heard from since December 3.
Western Australian police's Missing Persons and Homicide Investigations Unit is looking into the case and appealing for sightings of the 33-year-old former NZDF serviceman, who grew up in Ngaruawāhia and Perth and attended Hamilton's Fraser High School.
His mum, Sharon Adams, believes he is alive.
He has previous history of going off radar, she said, and believes that he's gone "walkabout" – a spiritual outback hike in Australian Aboriginal society.
"It's different in New Zealand, it's a little country. But it's a big place here," she told the New Zealand Herald from Perth.
"He's a quiet boy, he's a loner. He's always been like a Lone Ranger.
"But when he goes off, he doesn't bother anyone, he just goes off quietly on his own.
"He's just taking time out right now. What's going through his mind right now… I don't know.
"I said to the police, 'He's gone walkabout'. He's not stupid in the way of survival, but he's silly for not telling anyone [his plans]."
Adams believes her son suffers from depression and post-traumatic stress disorder (PTSD) brought on by his army experiences.
His father Howard Mahu served in the New Zealand Special Air Service Squadron as a driver.
Ray followed in his father's footsteps, serving in the Royal New Zealand Infantry Regiment's 1st Battalion, and completing a six-month tour of Afghanistan as a diesel mechanic. His brother Hayden Mahu earlier told the Herald that his brother had been close friends with 26-year-old Corporal Douglas Hughes, who took his own life while in Afghanistan in 2012.
"I think it might have affected him," Hayden said.
Their mum agrees. "That was tragic for him," she said. "It took him nearly three years to accept his best friend had died over there."
Five months after Hughes' death, Ray was convicted of failing to stop and refusing a blood sample when the Linton soldier drove through a police checkpoint.
His family say that his father's death in 2001 was a big blow for Ray, who was a teenager and in high school at the time. Shortly after, a close aunty and uncle – koro Jerry and "Nanny Kathy" – also passed away.
His mum says he's suffered a lot and believes he's near the coast trying to reconnect.
"We all have a tendency to head towards the water when we're feeling a bit low, and he goes there quite often when he's on a downer," she said.
Adams spoke to him on December 3 – the day he disappeared.
He'd been going through relationship issues but seemed "fine", she said.
Adams admits that her son had been in trouble in the past but quashed rumours that he was due to be deported, and other talk that he'd been responsible for a local crime wave over the last month.
"Ramon doesn't work like that. He wouldn't hurt anybody intentionally, unless he's under threat," she said.
She's going to see a psychic this weekend, desperate for answers.
"I've got to take something," Adams said. "I don't take them as gospel, but I take them as hope. I'm open to anything at the moment."
Asked if she had a message for her son, she said: "Come home. We've got a strong bond ... I don't need to tell him anything else – he knows. Just come home."
Ray is described by police as 182cm tall, of medium build, with brown skin and tattoos on his left arm, short black hair and brown eyes.
He could be driving a silver 2002 model Nissan Pulsar hatchback, registration number 1BGZ696.
• Anyone who sees Mahu or his vehicle or hears from him is asked to contact WA police on 131 444 from Australia or through www.crimestopperswa.com.au
