Rescuers searching for two teenagers who disappeared off Florida were "very concerned" to find their overturned boat but no sign of the boys, a Coast Guard official told NBC News in an interview.
The 19-foot, single-engine vessel was found capsized Sunday, two days after it was taken out by 14-year-olds Austin Stephanos and Perry Cohen.

"We are very concerned because we have found the vessel but not the boys," Coast Guard Lieutenant Commander Gabe Somma said Sunday. "We are searching around the clock 24/7, hoping to bring those boys home."
The boat was found 67 nautical miles off the coast near Daytona Beach. The city is some 160 miles north of the town of Jupiter, where Stephanos and Cohen were last seen Friday. One life vest was found in the hull of the boat but the boys' families said they did not know how many were originally on board.
"I just want them home. I know he's coming home. I just want him home now," Austin's mom, Carly Black, told NBC station WPTV.
Somma told NBC News there were "so many unknowns" in the disappearance. "Where did the vessel capsize? Where did they go in the water?" he said. "We are covering a large area and we are continuing to look."
The teenagers were last seen at 1:30 p.m. Friday and reported missing at 5 p.m. Thunderstorms in the area meant waters were likely rough between those times.
However, Somma added that "survivability is high" in the region because of warm water temperatures.
The boys' families have offered a $100,000 reward, and NFL Hall of Famer Joe Namath, who is the neighbor of Perry's stepfather Nick Korniloff, also appealed to the public for help.
"We'll keep on looking until we find them," the Super Bowl-winning quarterback said. "We're all praying. ... The good Lord's gotta help us out."
But despite these appeals, Somma told NBC News that the rescue effort "should be left to the professionals."