His family company had recently done a deal to sell the North West Regional Hospital in Burnie to the Tasmanian Government for $52 million.

The hospital has reaped the family about $90 million in lease fees over the past 16 years.

Apart from extensive Tasmanian holdings, they also have investments in several other states and in New Zealand - where Herman met his wife Victoria in the 1980s.

He has two brothers, Robert who lives in Hobart and Charles who was a dentist for 20 years in Geelong.

But when police found Herman Rockefeller's blue Prius sedan on a lonely road near Ballan yesterday afternoon, the mystery surrounding his disappearance took on a graver - perhaps more sinister - aspect.

The car was found near an abandoned homestead on Carween Lane, near the Werribee River. It had not been seen since it was driven from the long-term car park at Melbourne Airport shortly after 9pm on Thursday.

Mr Rockefeller, 52, had flown from Newcastle after a four-day business trip, earlier telling his family by telephone he would see them when he got home. He never arrived - and did not use the most logical freeway route towards his home in East Malvern.

Instead, it seems, the car headed west towards Ballan.

The inevitable buzz of speculation that Mr Rockefeller might have staged his own disappearance dimmed a little when the homicide squad was called in to assist the investigation yesterday.

But Detective Senior Sergeant Stuart Bateson said there was no indication that the car had been tampered with.

''There are no signs of foul play; the car was locked and secure,'' he said. ''We have no real conclusion about what has happened to Herman.''

Police stressed that the homicide squad presence did not mean they were looking for a body. But it underlined the increasingly serious fears held for the unassuming suburban property investor who happened to share one of the most famous surnames from America's Gilded Age.

If Herman Rockefeller had even a distant connection with his New York namesakes, there was no sign of it when he and his two brothers, Charles and Robert, arrived in Australia with their parents Herman senior and Enid in the late 1960s.

These Rockefellers were from Akron, Ohio, where they had owned a bakery, and they lived in Newtown, Geelong.

The boys went to school at Geelong College while their father started the first of a series of businesses that would make him wealthy - and set his sons on a course that would see them buy and sell their way into millions of dollars of property.

Charles Rockefeller yesterday said his brother had no history of mental illness or depression. ''He has a really positive frame of mind and such a love for life,'' he said.

He did not believe Herman had any connection to where the car was found. ''It's just a complete shock and mystery, I'm like a zombie in a fog.''

Herman Rockefeller's extended family gathered yesterday at the home he shares with his wife and two children in East Malvern.

''I have been thinking about all the various scenarios and I have no idea. It's the most baffling thing I've ever experienced. He's been a wonderful brother to me,'' Charles said. ''We are categorically, absolutely no relation to the Rockefellers in New York.''

Peter Blackmore, Mayor of Maitland in NSW, had met Herman and Robert Rockefeller for the first time on the day Mr Rockefeller disappeared.

The three had a meeting about the Pender Place shopping centre the brothers had purchased. Mr Rockefeller introduced himself as a ''long-term'' community investor.

''Honestly, there was nothing that would have indicated that there was a problem,'' Mr Blackmore said yesterday. ''They were both very buoyant and happy and in fact they talked about coming back in three weeks with their father.''

The archetypal quiet achiever, Mr Rockefeller made few impressions on those who knew him at school and university.

Classmates from Geelong College recall a pleasant, quiet schoolboy - dark-haired, chubby and small. He was a bright scholar who liked a laugh but had a mind of his own and could go off on a whim, according to one long-time friend.

The friend described Mr Rockefeller as a fitness fanatic and regular marathon runner.

As the sun set last night SES volunteers helped police conduct a line search of long grass in paddocks near where the car was found.

The scene was sealed off with tape and forensic technicians joined detectives in a painstaking search for a clue to a deepening mystery.

Mr Rockefeller's wife, Victoria, said there was nothing to indicate where he was.

''We have no idea at all. He's level-headed, the business is going well and he's a real family man. It's absolutely out of character.''