Milawa, a town of about 500 south-east of Wangaratta, is known to the family with youngest daughter Ella, 22, having ridden horses there.

Police are investigating three break-ins on Thursday at a local horse club, a football club and the general store.

The back door had been pushed open at each and food was taken from one.

It appeared that someone had tried to gain access to two cars parked out the front of the horse club.

It is not known if Mr Tromp was responsible and may have been trying to get supplies, but his family are hopeful it was him.

Mr Tromp, his adult children Mitchell and Ella have said, has strong survival skills. They are confident he will be found.

Despite speculation the family suffered a shared delusional disorder before and during their "technology free" road trip, son Mitchell, 25, told Fairfax Media there were no recent or current psychological diagnoses in his family.

Paranoia over financial affairs - or that someone was trying to steal their money - are believed to be the catalyst for triggering the family crisis.

It is understood the paranoia built up to a point where Mr and Mrs Tromp became terrified someone was coming after them and then made the ill-fated decision to leave the family home in Silvan, in the Yarra Ranges north-east of Melbourne, last Monday.

Monbulk sergeant Mark Knight, who works with Mr Tromp's brother and knows the family, said no one was after the family and they were not being followed.

He has said previously there were no diagnosed mental health conditions and there is no evidence of drug taking or drug psychosis.

The family have no debts and their businesses - an earth-moving company and berry farm - are successful.

Mr Tromp's brother Ken Tromp, a policeman based at Yarra Ranges station Monbulk, is understood to be in the north-east searching for him with other relatives.

The active effort to find him is now being primarily conducted by his family rather than Victoria Police or the SES.

Residents in the north-east, particularly farmers, have been urged by his family to keep a look-out for him.

With 19.2 millimetres of rain overnight on Friday, it is possible Mr Tromp may have sort shelter in sheds on farms in the area.

The last credible sighting of Mr Tromp remains the one in Wangaratta on Wednesday night where he was seen by a young couple walking away from his car into parklands. The keys were left in the ignition.

His wife Jacoba and eldest daughter Riana remain in hospital in Goulburn being assessed by mental health practitioners. Relatives have travelled to Goulburn to be with them.

Mitchell, 25, appealed to the public for help to find his father on Thursday.

"I've never seen anything like it. It's really hard to explain or put a word on it but they were just fearing for their lives and then they decided to flee," he said.

"It was a build-up of different, normal, everyday events — just pressure — and it slowly got worse as the days went by."

"I've never seen anyone like this or anyone conduct themselves in this way. I just really want my dad to be found."

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

Timeline

Monday, August 29: The Tromps leave the family home in Ella's Peugeot, terrified someone was after them. 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 in desperation 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. The couple drive south to Wangaratta where they separate. Jacoba takes public transport to Yass and Mark is seen leaving the Peugeot, with keys in the ignition, in a side street.

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 walking away from the car. It is believed this man was Mark. Later in the day, Jacoba is taken to Yass District Hospital after a local found her wandering around town.

Saturday, September 2: Police are investigating several reports of break-ins. Three in Milawa on Thursday where food was taken and another at a motel in Wangaratta on Wednesday night. It is not known that Mark was responsible, but the family believe it was him. The focus on the search remains in Wangaratta.