The 12,800-dwt Fair Artemis (built 2008) was 60 miles off the coast with a 24-strong crew and a cargo of gasoil at the time when it last made contact on Wednesday.
Greece's Fairdeal Group told TradeWinds it has been trying to re-establish contact.
The company criticised alarmist reports from the IMB and said no one yet knew what had befallen the vessel.
It