The last contact with the 12,800-dwt Fair Artemis (built 2008) was made on Wednesday, 60 miles off the coast of Ghana.
"The vessel is not in our waters," a navy spokesman told AFP. "It's gone off and they suspect it's moving towards Togo. The navy is trying to get confirmation from the Togolese if they have identified any vessel."
The Fairdeal Group-operated tanker has 24 crew on board and a cargo of gasoil.
