"I felt a kick to the back of my seat. I turned around and saw two legs stretched across the back between my seat and the floor," Mr Whittaker told the Goulburn Post.

"She was lying on the floor" 

"She did not know her name and had no idea where she was."

The distressed and disoriented young woman turned out to be Riana Tromp, the elder daughter of Mark and Jacoba Tromp.

in the grips of a mysterious existential crisis, the Victorian couple had fled their home in the Yarra Ranges hamlet of Silvan, in Melbourne's outer east, and pursued by who knows what headed north with their three adult children for the border and beyond.

On Monday, Mr and Mrs Tromp and their children Riana, Mitchell and Ella had piled into Ella's Peugeot for a "technology-free" trip to NSW.

Come Thursday four family members had emerged shell-shocked in four separate locations and one was still unaccounted for.

Despite unconfirmed reports of Mark Tromp being seen on both sides of the border on Thursday and Friday, and possibly breaking in to aWangaratta motel on Thursday evening, the only verified sighting since his family last saw him was on Wednesday night.

On Friday Goulburn police said Mr Tromp had been sighted near the NSW town of Bega, more than 500 kilometres from Wangaratta. Bega police, however, said they had investigated the sighting and it was incorrect.

On Thursday, Mitchell Tromp likened the sequence of events on the family's ill-fated road trip to a scary movie, with a build-up of pressure and paranoia in his parents spreading before, one-by-one the Tromp children bailed out.

"It slowly got worse as the days went by. They were just fearing for their lives, and then [we] decided to flee," he said. 

Riana, 29, the young woman who wound up in the back of Keith Whittaker's ute, left her parents at the Jenolan caves.

"I got an extreme shock," Mr Whittaker said. "I pulled over in a rest area.

"About 20 minutes later the young woman sat up and was staring straight ahead. I asked her who she was and if she was all right? She did not know her name and had no idea where she was.

"I asked her if she needed any water or anything or was in any way injured and she said no.

"Then I called the police. Until the police arrived, she mostly sat and stared straight ahead as if she was catatonic.

"They arrived about an hour later and took her back to Goulburn Police Station.

"She was a well-dressed young woman and she offered to give me $50 for my trouble but I said no thanks. I was just glad to help her."

A NSW police spokesperson confirmed the young woman was Riana Tromp and that officers had collected her from Mr Whittaker near Lake George at 2pm on Tuesday.

They said she and sister Ella, 22, had stolen a car from Jenolan Caves and driven it to Goulburn, before Riana alighted and entered Mr Whittaker's ute. Ella kept driving back to Victoria.

Police also confirmed on Friday the young woman had since undergone a mental health assessment and was now in the care of mental health services in Goulburn.

Mark Tromp was last seen running away from his daughter's ditched Peugeot in Wangaratta by a young couple who say they were 'stalked' by him in a bizarre cat-and-mouse through the streets of the north-eastern Victorian country town. A break-in at a motel on Thursday night may indicate he had not left the city, theBorder Mail reports

Police could not confirm if the culprit was Mr Tromp.

Rosemarie O'Neill manager of Miller's Cottage said staff discovered the break in on Friday morning, but the room had not been damaged.

"We called the police because we thought it could help them look for that missing man," she said.

"We all want him to come out and be OK."

Police confirmed they were fingerprinting a room after the door was found ajar at 9.30am today.

The bathroom had been used, the bed looked to have been used and a muesli bar wrapper was on the floor, police told Fairfax Media.

Mr Tromp's family members had travelled to Wangaratta to help with the search, driving around and talking to people in hope of getting any information.

His cousin, who did not want to be identified, said the family's investment properties in Wangaratta were being rented out and he had no idea where to look.

"We've been looking everywhere, we were up late [Thursday] night and up again at 5.15am [Friday] morning," he said.

"I don't think he's been able to walk through Wangaratta without being seen."

The cousin described Mr Tromp as "a normal, hard-working, honest family man" and said the paranoia of recent days was "so far out of left field".

"I've been working with him and I saw no sign of this," the man said.

"It's horrible … He's by himself and obviously thinks someone's after him."

Sergeant Mark Knight, of Monbulk police, said two sightings of Mr Trump on either side of the Victoria/NSW border were both days old.

"We haven't substantiated any sightings," he said.

"I don't know where he is, I've got no idea."

Mr Tromp's wife Jacoba had spoken to police and family from hospital in Yass, where she was found on Wednesday, but was yet to shed any light on what happened.

"We'll continue to talk to her, but we just have to let her rest for now," Sergeant Knight said.

Police said on Friday morning they have had several reports from people who believe they have seen him. None have been verified and the Wangaratta sighting remains the only concrete lead.

There is no record of Mr Tromp leaving Wangaratta by train or bus and there have been no reports of cars being stolen.

A shell-shocked Mitchell – the middle Tromp child – pleaded for his father to come home in a press conference on Thursday.

"I just really want my dad to be found," he said.

"He's not dangerous, he's my mate, my father. I love him."

"I've never seen anyone like this or anyone conduct themselves in this way".

Sergeant Knight, said he knows the family and say they have no diagnosed mental health problems. There is no evidence of a drug-induced psychosis or drug taking.

No one in the family has accessed a doctor or psychologist recently or been issued a prescription, he says. They do not belong to any churches or sects and do not have debts.

Two of the children live at home and all three work seven days a week in the family's successful businesses – a berry farm and an earthmoving company. Daughter Ella has her own company as well supplying trucks and drivers to Yarra Valley farms.

The family moved to Silvan from nearby Macclesfield 10 years ago.

Mr Tromp's brother Ken is a police sergeant in Monbulk and is believed to be helping in the search for his brother.

"I am asking myself 'what is going on?'," said Sergeant Knight. "It's a mystery. But there's nothing sinister."

Sergeant Knight said when he checked their home after the first reports of Riana being found near Goulburn, the house was open and keys were in car ignitions but there was no sign of any struggle.

"This is just a massive meltdown, I'm sure of it. Something triggered them."

Timeline

Monday, August 29: The Tromps leave the family home in Ella's Peugeot to go on a technology-free road trip. During the course of the drive, it's discovered Mitchell has brought his phone with him. He throws it out of the window near Warburton, about 32 kilometres from the family home. The family continues driving towards Bathurst.

Tuesday, August 30: Mitchell decides he wants to go home. He leaves the family at Kelso, a suburb of Bathurst, about 7am and makes his way to Sydney. The rest of the family continue on to the Jenolan Caves. That afternoon, they decide to split up. Ella and Riana steal a car and make their way to Goulburn then go their separate ways. Riana is found along the highway after stealing a lift in a ute and is taken to the local hospital due to stress-related issues. Ella drives back to the family home in Silvan. Parents Mark and Jacoba are reported missing and that afternoon police attend the family home to find credit cards and mobile phones lying around the house and car keys in ignitions.

Wednesday, August 31: Mitchell arrives at the family home in the morning after catching the overnight train from Sydney. That afternoon, police search the Jenolan Caves area for Mark and Jacoba but are unable to find them.

Thursday, September 1: Police are notified in the early hours of the morning that the family car has been located in Wangaratta and that a lone man was seen running from the vehicle. It is believed this man was Mark. Later in the day, Jacoba presents herself to Yass District Hospital after a local found her wandering around town. Police continue to look for Mark during the evening, and have no reason to believe he has left the Wangaratta area.

smh.com.au, goulburnpost.com.au, with Chris Johnston and Tom Cowie.