Former delivery boss Ralph Christie, 53, used more than Â£600,000 to fund his gambling habit, Bradford Crown Court heard.
The frauds, involving more than Â£1m, were carried out between March 2007 and May 2009.
He was jailed for seven years for five counts of fraud.
Christie, of North Road, Ripon, North Yorkshire was found guilty on Thursday after a six-week trial.
He convinced two of his victims, Michael and Kimberly Thompson from Doncaster to invest Â£200,000 in his property development firm on the island of Crete.
Christie had promised the Thompsons, who were planning semi-retirement on the Greek island, a 25% return on their money.
Later, the couple tried to get their money back but were met with excuses.
"We got so much back but then the rest of it never came," they said.
The Thompsons described Christie as a "remorseless" man "living off other people's money".
"It was like we were in mourning, it was like we'd lost a close family member," Mrs Thompson said.
"Some days I couldn't get out of bed."
A "remorseless" property developer who convinced his victims to invest in a bogus Greek property scheme has been jailed.