Most of them were attempting hikes under the scorching sun as much of Greece saw record temperatures for the first week of June, reaching 43C (109F) in many areas of the country.
Meteorologists have noted it was the earliest heatwave – which for Greece means temperatures exceeding 38C for at least three days – on record.
Dimitris Kalatzis, who led the Samos search team, told Greek media that rescue missions were often made more difficult because foreign tourists go in search of tourist sites, unaware of the dangers of walking in the heat, and get lost.
On Friday, local authorities began searching for the two French tourists after one of them sent a distress message to the owner of the hotel where she was staying.
On the rugged island of Amorgos, an intense search is continuing for another American tourist, 59-year-old Albert Calibet, who went missing during a hike on the small island last week.
A former deputy with the LA Sheriff’s Department, Mr Calibet has been missing since Tuesday.
Mr Calibet had travelled to the island from Los Angeles. An experienced walker, he set off from the village of Aegiali in the north at around 7am for the port of Katapola, a path that normally takes around four hours by foot.