CBS News correspondent Kelly Cobiella reported Bruce O'Krepki went over the tenth floor rails off the Carnival Fantasy on Sunday night about 150 miles southwest of Tampa, Fla.
The Coast Guard says the search continued overnight into Tuesday.
O'Krepki was with about 35 former classmates on the ship after graduating recently from St. Thomas Aquinas High School in Hammond, La. WWL radio in New Orleans reported that his parents were chaperoning the trip.
The ship had left New Orleans and was en route to Key West.
O'Krepki's disappearance, Cobiella reported, has left his community stunned.
"Good youngster, great attitude," said John Cox, O'Krepki's St. Thomas Aquinas soccer coach. "In fact, he was my captain this year. ... When a person connects so much with a community, his family and himself, it's a huge burden for everybody."
Family and friends gathered at Hammond Church on Monday, Cobiella said, united in their grief, but praying for O'Krepki to be found.