Today however, there has been speculation the crew was killed.
This is what the BBC is reporting.
The two Danes and four Filipinos are now thought to be held on a captured Taiwanese fishing boat, the Shiuh Fu No.1, an EU naval official said.
Pirates in two skiffs attacked the Danish-flagged M/V Leopard on Wednesday but later took the crew off the ship.
Nato sailors searched the abandoned vessel. Its cargo is said to be intact.
The Nato sailors from a Turkish warship, the Gaziantep, boarded the M/V Leopard on Thursday, when it was found to be drifting.
It is not clear why the ship was immobilised, said a spokesman for the EU's Navfor anti-piracy mission.
"We believe the ship was carrying arms, ammunition and explosives, and we believe the cargo is still intact," said the spokesman, Wing Commander Paddy O'Kennedy.
The international naval forces refrained from attempting a rescue as a radio message picked up while the pirates were on board warned them to stay away, he said.
The M/V Leopard is reported to be about 810km (500 miles) from Oman's port of Salalah.
The ship's owner, Shipcraft, says "our main focus is now on the safe return of our crew; however, at present we do not hold any reliable information as to their whereabouts".