The two friends and firefighters launched their boat off the Florida coast Friday, headed out for an afternoon of fishing to honor one of the men’s recently deceased father, family members said.

But Fairfax County, Va., firefighter Justin Walker and Jacksonville, Fla., firefighter Brian McCluney never returned, sparking a desperate search by local, state and federal agencies and a flotilla of volunteers that entered its fourth day Monday. As of the evening, the search continued, and authorities announced the discovery of a tackle gear bag belonging to McCluney.

Nearly 40 boats and some aircraft were scouring a section of the Atlantic stretching from Brunswick, Ga., to St. Augustine, Fla., Jacksonville Fire Chief Keith Powers said at a Monday evening news conference. The U.S. Coast Guard estimated searchers had combed more than 24,000 square miles of ocean in recent days.

“We’re just all very hopeful,” said Kari Futch, a relative of Walker who is in Florida with other family members. “They are both survivors. They are good on the water. We want them home and out of the elements.”

Futch said the last time family members heard from Walker was shortly before he and McCluney left for the trip from Port Canaveral, near the Kennedy Space Center and midway down Florida’s Atlantic coast. Futch said the pair launched in McCluney’s father’s 24-foot boat around 11 a.m., headed for a fishing spot about 15 miles off the coast known as the “8A” reef.

The pair were supposed to return at 6 p.m. Friday, but when they did not show up by 8 p.m., family members alerted authorities, Futch said. Neither man has responded to calls. Futch said a tracking app last recorded Walker’s location near the 8A reef around 1 p.m. Friday.

Searches have carried on since the pair were reported missing, said Coast Guard Petty Officer Ryan Dickinson, but it remained unclear what happened to the boat. Powers said Monday evening that a volunteer vessel discovered a gear bag about 50 nautical miles off the coast that family members believe belonged to one of the men. The Coast Guard was diverting search vessels to the area.

Dickinson said no distress signal was received from the vessel. McCluney’s wife, Stephanie, said in media interviews that the boat had broken down in the past and speculated that might have happened this time.

The search has generated national attention and drawn an outpouring of support. Volunteers are plying the seas with their own boats, along with vessels and aircraft from the Coast Guard, Navy and U.S. Border Patrol, among others. Thousands of dollars have been donated to help with the search.

“All search and rescue cases are different, but this one seems to have hit home with a large number of people,” Dickinson said.

Futch said Walker is originally from Florida and has been a Fairfax County firefighter for seven years. He is married and lives in the Dumfries area. Futch said he is a motorcyclist and volunteers with the Strength and Honor Motorcycle Club. Walker’s dream was to be a firefighter.

“He has an amazing personality,” Futch said. “Always energetic and happy. Always wants to help people.”

Fairfax County fire officials said Walker is a master technician stationed in Franconia. They said some Fairfax County firefighters traveled to Florida to assist in the search for the missing men.

“We remain optimistic they will be found,” the department said in a statement Monday.

Powers said McCluney is married, has two children and is a decorated Navy veteran. Powers said both men were well trained to survive on the water.

Futch said the outpouring of support has been heartwarming.

“The ocean and the air are saturated with average people who want to help,” Futch said.

Magda Jean-Louis contributed to this report.