The U.S. officials said the two crew members were the captain and chief engineer, CNN said.
The attack on the oil platform supply vessel C-Retriever occurred in the Gulf of Guinea off the port city of Brass.
Details about the attack, the conditions of the kidnapped men or the vessel's condition weren't immediately available.
The C-Retriever is owned by Edison Chouest Offshore, based in Louisiana.
The oil-rich Gulf of Guinea has drawn attention as a piracy hotbed recently, with more than 40 pirate attacks reported through September, the International Maritime Bureau said. The bureau said 132 crew members have been taken hostage.
U.S. Marines were in the region aboard a Dutch ship, CNN said.
Forces from the United States, Britain, Spain, the Netherlands and five African countries recently conducted exercises off the west African coast meant to help strengthen maritime security, the U.S. Navy said.