The yacht Quest was hijacked on Friday off the coast of Oman, and officials had said Tuesday it was less than two days from the Somali coast, according to CNN.
The U.S. Navy had said it was prepared to intervene to rescue the Americans — believed to be California couple Scott and Jean Adam, who own the yacht, and Phyllis Mackay and Bob Riggle.
The Quest had been taking part in international yacht race, but went off in a different direction on Feb. 15, according to the organizers of the race, the Blue Water Rally.
Somali pirates usually attack commercial ships instead of yachts. They have made hundreds of millions of dollars seizing merchant ships for ransom in recent years.
However, pirates held a British couple, Paul and Rachel Chandler, in Somalia for more than a year after seizing their yacht in October 2009.
International naval patrols off Somalia's coast have had little success in stopping pirates from attacking ships in the Gulf of Aden and Indian Ocean.
The U.S. military was prepared to intervene in the situation if necessary, according to the deputy commander of the U.S. Navy's Bahrain-based Fifth Fleet based, Rear Adm. Charles Gaouette.
"They were part of a sailing group that set sail from the southern tip of India into the western Indian Ocean," he told CNN, adding that the situation was being monitored with U.S. Central Command.
Gaouette said there is no reason to believe the hijacked yacht had been taken to the coastline of Somalia yet, though pirates in the region have been known to do so.
Pirates hijacked the Quest two days after a Somali pirate was sentenced to 33 years in prison by a New York court for the 2009 hijacking of the Maersk Alabama. That case ended in a spectacular rescue when Navy sharpshooters killed two pirates holding the ship's captain, Richard Phillips.
The pirates are unlikely to hurt the four Americans because they won't win any ransom money if they do, Graeme Gibbon-Brooks, the head of Dryad Maritime Intelligence, told the Associated Press. He said the pirates would be wise to abandon the yacht because the hijacking threatened their business model, which is essentially holding large shipping and insurance companies to ransom.
"They risk the collapse of their business model if they change their status quo and the American government deems that they pose an immediate threat to the safety of American citizens," he said. "They've made a mistake and it's in the Somalis' business interest to get off the yacht as soon as possible." Estimates vary, but the pirates are believed to currently hold at least 31 vessels and about 700 hostages.