A Coast Guard helicopter and a jet joined the hunt along with two 110-foot cutters that unsuccessfully searched through the night Friday.
Eight bodies had been recovered and nine people rescued, including two children, after a boat apparently trying to smuggle Cubans into this country capsized Thursday night in choppy Atlantic waters more than 22 miles (35 kilometers) south of Miami.
After interviewing the survivors, the Coast Guard clarified that they believed in all 23 people were on board the boat.
Rough seas with with swells of 8 feet (2.4 meters) made the search for survivors difficult overnight.
"Right now, conditions cannot warrant an effective search," Petty Officer Tony Wells said late Friday night.
Nevertheless, he said, the two cutters were making sweeps in Atlantic waters offshore from Miami north 30 miles (48 kilometers) to Fort Lauderdale.
"Keep in mind, this is the Gulf Stream, everything will float north," Wells explained.
The 29-foot (8.5-meter) Wellcraft boat went down late Thursday off Elliott Key, in 6-foot (1.8-meter) seas.
Friday night, Cuban-Americans who thought they might have relatives on the boat were awaiting word from the Coast Guard.
"There's no way to describe the feeling because, right now, you don't know if he's dead or alive," said Manny Rodriguez.
A freighter rescued seven adults and two children from the half-submerged boat Friday morning. The survivors managed to hang on for about 10 hours, according to Coast Guard Petty Officer Scott Carr.
The Florida-registered boat was sold two weeks ago to a man named Francisco Gomez, whose relatives said he hasn't been seen for two or three days, television station WSVN reported Friday.
Carr acknowledged the boat may have been operated by smugglers who charge Cubans to bring them to the United States. The Border Patrol identified two of the survivors as smuggling suspects and initiated a criminal investigation.
"We have no record of any smuggling episode with a higher fatality rate" in waters stretching from Key West to the Carolinas, said Daniel Geoghegan, an assistant chief with the Border Patrol.
Cubans intercepted at sea routinely are returned to Cuba. So far this year, 927 Cuban refugees have been intercepted off South Florida.