Florida teens Perry Cohen and Austin Stephanos have been missing since Friday.
"People can survive in the water," said Capt. Mark Fedor, chief of response for the Coast Guard 7th District. "It's relatively warm, but, again, it's a dangerous environment, and there's only so long you could stay in the water."
The search area now stretches from where they boys left -- Jupiter, Florida -- up to Charleston, South Carolina.
The Coast Guard said five cutters, a Navy ship and multiple planes are involved in the search.
The situation has grown increasingly dire since the boys' capsized boat was found Sunday, but their families are not giving up hope.
"We are 100% committed to finding and rescuing those boys, as is the Coast Guard, and we will not stop until we get them back home with us," Perry's mother, Pamela Cohen, told CNN's "Erin Burnett OutFront" late Tuesday.
"We just feel very, very confident that they will be able to stick through this. They know that we're coming for them and we will get them," she said.
Mothers hold out hope
"They've brought out every resource they have," Carly Black, Austin's mother, said of the Coast Guard search. "They're using everything they have to find our boys. They truly believe they're going to find them."
The boys left Jupiter on Friday in a 19-foot, single-engine center-console vessel. Later that day, when one of the boys' grandmothers didn't hear from them, she reported them missing.
While the boys are young, they were legally operating the boat. Florida regulations say a person must be at least 14 to operate a watercraft.
"We know our boys. We know the determination and the courage that they have. We know the skills that they have. We know how athletically fit and able they are. Both of our boys learned how to swim before they learned how to walk," said Cohen.
A community rallies
The Jupiter community rallied as the search for the teens continued. Residents held a prayer vigil Tuesday night on Stuart Beach.
Nick Korniloff, Perry's stepfather, said the family had rules about where Perry could take a boat without adult supervision.
"We requested when he was out in the water, that he fish the river and Intracoastal (Waterway)," he said Monday. "He could go as far as the rocks and inlet."
Perry was told not to go into the ocean unless he was in a bigger boat and had an adult with him, Korniloff said.
"We have taught them the respect of Mother Nature, the power of the sea," he said. "They know what the water is all about."
Football great Joe Namath, a neighbor of the boys' families, is among the friends supporting them. He also said he's optimistic.
"The history of the high seas have survival rates over the years," Namath said. "There have been miracles out there, and we're planning on finding the children."
Keith Judy is one such survivor. He and a friend spent 20 hours in the ocean with his son and the son's friend on July 13 after their fishing boat capsized off Charleston, South Carolina, Judy said Tuesday on CNN's "New Day."
He said the group tied itself together with a rope and hung onto a floating cooler through the night.
"Before the Coast Guard found us, the sharks started bumping us and swimming through our legs and actually hitting our skin and cutting our skin," Judy said. "We fought off small sharks for a little while."
Judy said he got the attention of a Coast Guard boat by standing on the cooler and waving a life jacket.
The search area
Austin and Perry were last seen near Jupiter buying $110 in gasoline for their boat, Coast Guard Petty Officer 1st Class Steve Lehmann said at a news conference.
The teens' boat was found Sunday, capsized 67 nautical miles (about 77 miles, or 124 kilometers) off Florida's Ponce de Leon Inlet.
The latest search area was based on the location of the boat, using flow models, Lehmann said.
The Coast Guard said Tuesday that it had completed search patterns covering more than 30,000 square nautical miles.
$100,000 reward offered
The boys' families are offering a $100,000 reward for their rescue and are asking citizens to help by looking for debris along the beach.
Lehmann said the Coast Guard discouraged volunteers from getting involved in the search itself because they could hinder the guard's activities.
The discovery of the capsized boat, he said, means the missing teens could be in a more serious situation than officials feared.
It's unknown whether the boys are wearing life jackets.
"It's one thing for the boys to be missing inside the vessel, and it's another thing for them to be missing in open water. ... Now they're in an even worse situation if they are to be in the water right now," Lehmann said.