CLEARWATER, Fla. -- The Coast Guard searched off Florida's Gulf Coast on Sunday for a fishing boat carrying NFL players Corey Smith and Marquis Cooper and two other men who were missing for nearly a day in choppy seas.

Smith, a defensive end for the Detroit Lions, and Cooper, an Oakland Raiders linebacker, were on a 21-foot vessel that left Clearwater Pass for a fishing trip Saturday morning, but they didn't return as expected, the Coast Guard said Sunday. Crews used a helicopter and an 87-foot ship to search a 750-square mile area west of Clearwater Pass, but poor weather made the search difficult. Officials didn't receive a distress signal from the missing craft.

Cooper owns the boat, and he and Smith have been on fishing trips before, said Ron Del Duca, Smith's agent. Cooper and Smith were teammates on the Tampa Bay Buccaneers in 2004. Two others were aboard: Will Bleakley and Nick Schuyler, both former University of South Florida players.

Coast Guard Capt. Timothy M. Close said the weather early Saturday had been fair but worsened toward the evening as a front still battering the area moved in. The National Weather Service said seas were about 2 to 4 feet Saturday morning and increased to 3 to 5 feet in the afternoon. Late Saturday night, a small craft advisory was issued, when winds were around 20 knots and seas were up to 7 feet or more. There were no thunderstorms in the area.

Close said the men were traveling in a boat manufactured by Everglades. At least one of the men was an experienced boater, and relatives provided the Coast Guard with GPS coordinates from previous fishing expeditions.

Close said there was no communication with the men even before the weather started to pick up. They were expected home by early evening. No sign of them or the boat had been spotted by late Sunday afternoon. Relatives told the Coast Guard the men had lifejackets and flares onboard.

Poor weather conditions could be dangerous for a boat the size of Cooper's.

"A 21-foot boat is a relatively small vessel to be 50 miles off shore in bad weather conditions, certainly the current weather conditions," Close said.

Close said there was no sign yet that the men sent a distress signal.

"That's not to say they didn't send one out," he said. "We didn't receive anything."

Danielle Mayes, owner of Jaxson's Bait House near the ramp where the men departed, said Saturday had been deceptively beautiful. The weather was warm, and boaters had packed the small parking lot overlooking seaside condominiums and light blue waters. Mayes said many of the boaters who returned Saturday evening, after the weather picked up, said they were surprised that the water had become so rough.

The Coast Guard search was mainly by air and was hampered by the poor weather, Close said. He said there were 14-foot seas offshore and wind gusts of up to 30 mph. Water depth in the search area ranges from 20 to 50 feet. The Coast Guard originally sent a 47-foot ship to search for the men around 2 a.m Sunday. It returned to dock about eight hours later and was replaced by a larger ship, in part because of the weather.

Smith, 29, had 30 tackles, including three sacks, and one interception in 12 games last season for the winless Lions. Smith, who is 6-foot-2 and 250 pounds, also played for the San Francisco 49ers and played college ball at North Carolina State. He lives in Richmond, Va.

Del Duca called Smith one of the "good guys" of the league and said he was planning to start visiting teams as a free agent this week. Del Duca said he has spoken with Smith's family and also is in touch with Coast Guard officials.

"They've assured me that they're deploying all available resources to look for these guys and get them back," he said.

Cooper, 26, has played five seasons with the Buccaneers, Seattle Seahawks, Jacksonville Jaguars, Pittsburgh Steelers and Raiders. He appeared in 26 games with the Buccaneers in 2004 and 2005, recording 30 tackles. He has played sparingly since as he has bounced between teams, appearing in 13 games and recording 10 tackles.

Cooper, who is 6-foot-3 and 230 pounds, played college ball at Washington. His hometown is Mesa, Ariz., and his father, Bruce, is a prominent sportscaster for KPNX-TV in Phoenix.

Cooper told The Seattle Times in 2002 that one reason he chose Washington was the abundant fishing.

"I like fighting the fish," Cooper told the newspaper. "And just relaxing out there and being alone and being outside."

Lions spokesman Bill Keenist and Raiders senior executive John Hererra said the teams are monitoring reports on the players.

While the search continued, Cooper's pickup truck and boat trailer remained in the parking lot near the boat launch. On the dashboard was a one-day parking receipt that expired Sunday morning.

"Please contact the Coast Guard," read a note left tucked underneath a windshield wiper. "Someone was worried about your welfare."

Copyright 2009 by The Associated Press