(CARACAS, Venezuela) -- The son of Italian fashion mogul Vittorio Missoni says a plane crash is the "least plausible" explanation for his father's disappearance off the coast of Venezuela, hinting that he might have been kidnapped.
Venezuelan authorities have been searching since the twin-engine plane was lost last Friday near the resort islands of Los Roques. On board were Missoni, three other Italians -- including his wife -- and two Venezuelan crew members.
Missoni's oldest son, Ottavio, told Italian newspaper Corriere Della Sera on Wednesday, "A plane cannot vanish in this way, on a short route, without leaving any trace. I remain convinced that the least plausible reason is that they crashed into the water."
His opinion is based on a mysterious text message apparently sent from the cellphone of Guido Forsti, who was on the plane, to Forsti's son more than 48 hours after it disappeared.
Ottavio told the newspaper the text message read, "Call now. We are reachable."
He said he has even reached out to his father's potential enemies in search of any explanation.
Venezuelan officials said more than 400 people in boats, planes and helicopters searched Wednesday for a sixth day without success. No wreckage or debris has been found and Venezuelans will suspend the search after Thursday. An Italian team that assisted in search efforts last year with the Costa Concordia shipwreck is set to arrive in Venezuela later Thursday to help.
"It's really hard to believe the airplane isn't in the water," John Nance, ABC News' aviation analyst, said. "By the same token, unless you find wreckage, there's no proof it hasn't flown off someplace else. But I find that hard to believe."
Corriere Della Sera published the last known image of Missoni, 58, and his friends moments before they boarded the plane in Los Roques last Friday, bound for Caracas.
Thirty minutes after takeoff, the plane vanished into the Caribbean, leaving the tight-knit Missoni clan anxiously waiting for answers.
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