"Authorities conducted a thorough ground and air search of the crash area Sunday afternoon and into the night," a SGA spokesman said in a statement. "They are certain there were no survivors."
The family was flying from Flagstaff to Scottsdale Air Park when the crash occurred.
The cause of the crash has not been determined. Thomas Little, an air safety investigator for National Transportation Safety Board, said that it could be nine months to a year before a cause, if any, is determined.
Little said that there was a ¾ mile debris trail leading up to the crash site, indicating that pieces of the aircraft had come off. Little said the pieces appeared to come from one of the helicopter's rotors, although he could not say which one. Little said that he was not aware of any radio distress calls before the crash.
As soon as Tuesday investigators may start moving the debris to a salvage site to examine it and try to piece together answers.
"It's a time-consuming process," Little said.
A spokesman for the NTSB said none of the victims have been identified.
But a spokesman for the Scottsdale-based company that owned the aircraft said that three of the dead are Stewart, 64, his wife Madena, and their young daughter, Sydney.
Stewart was founder and chief executive of Service Group of America, a company that specializes in real-estate and food services.
"He was a real renaissance man, a business genius. He's already greatly missed and there's just such a huge hole here right now," said Brad Parker, the company's vice president of communications.
Stewart owned a ranch in Flagstaff, according to Metropolitan King County Council member Pete von Reichbauer, who was a former neighbor of Stewart on Vashon Island and worked for Stewart as a former vice president of SGA.
The helicopter belonged to Services Group of America, a large privately held company headquartered in Scottsdale and the parent company for Food Services of America. The firm was based in Seattle until 2006.
Stewart's longtime pilot also is among the dead, von Reichbauer said.
Stewart, who owned a house in Paradise Valley, Ariz., as well as an estate on Vashon Island, moved SGA's headquarters after the Washington Legislature enacted a new inheritance tax.
"The impact was horrific. There was debris everywhere," said Maricopa County Sheriff's spokeswoman Lindsey Smith. "The plane is literally in pieces."
According to emergency calls made from the scene, Smith said there were reports of smoke, loud noises and pieces falling from the helicopter as it went down.
"The indications are there were some mechanical issues going on," Smith said. She said the helicopter crashed in a wash that is about 100 feet wide, with houses on either side.
Cave Creek resident John Hoeppner, who lives about 200 yards from the crash site, was at home chatting with his wife, Cheri, when they heard what she described as "an engine cutting out" overhead. "It literally shook the windows in the house," Hoeppner said.
By the time he ran to the crash site, the helicopter was aflame. Hoeppner said he could see only large plumes of smoke and three bodies.
Sheriff deputies were going door to door, interviewing residents and blanketing a debris search area that officials described as several hundred feet.
Investigators with the Federal Aviation Administration and the National Transportation Safety Board were headed to the crash scene, FAA spokesman Ian Gregor said.
Services Group of America, of which Stewart is chairman and sole owner, is a holding company with combined annual sales of more than $2.5 billion and a payroll of more than 4,000 people.
Stewart is a Seattle native and was active in both Washington business and political circles. He used to host annual picnics on his Vashon Island estate for the Republican Party of King, Pierce and Snohomish counties.
He also unsuccessfully fought with the city of Seattle over building a helipad on the roof of his West Seattle office building, taking the matter to the state Supreme Court.
In part because of his battle with the Seattle City Council, he secretly funneled campaign donations to a 1995 ballot measure to change the way council members are elected. He was investigated and ordered to pay $62,000 in civil penalties.
A subsequent federal investigation resulted in Stewart paying $5 million in fines for funneling $100,000 in illegal contributions to Republican candidates through his employees. He also was sentenced to 60 days of home detention and ordered to work 160 hours in a homeless shelter. He was allowed to travel to work during his confinement but was barred from using his helicopter.
Stewart built Services Group out of a disparate group of businesses — food distribution, insurance, travel and others — he had acquired while running Stevedoring Services of America, one of the nation's biggest port operators. The two companies were separated in 1989.
He built up Services Group to be one of the largest private companies in Washington. But Stewart also developed strong ties to Arizona, owning property there for many years.
He changed his residency to that state in April 2005. He moved his company there a year later.
Information from Seattle Times archives and The Associated Press is included in this story. Seattle Times reporters Drew DeSilver and Susan Kelleher contributed to this report.