A tackle bag belonging to one of two firefighters who never returned from a fishing trip off the coast of Florida on Friday was found Monday amid a massive multi-agency search.

Brian McCluney, a member of the Jacksonville Fire and Rescue Department, and Justin Walker, a Fairfax, Virginia, firefighter, were last seen leaving a dock near Port Canaveral in a 24-foot fishing boat, according to the U.S. Coast Guard. They were reported missing after they did not return home Friday night as expected.

McCluney's wife, Stephanie Young McCluney, wrote on Facebook Monday that search crews had found her husband's tackle bag about 50 miles off the coast of St. Augustine, which is more than 100 miles north of Port Canaveral.

Coast Guard Sector Capt. Mark Vlaun confirmed during a news conference Tuesday that the bag, found by a volunteer, belonged to McCluney, and said "today's efforts are focused around where that equipment bag was found."

"I wholeheartedly believe this is a breadcrumb they threw overboard to say 'we are here, come find us,'" Young McCluney wrote. "I am standing firm on my face in prayer and that this be our Lord and savior guiding our path."

She told NBC News that the couple's two children have been asking why it's taking so long for their dad to come home. But "we are holding strong. These two men have the knowledge, they have the will, they have the stubbornness, and the drive," she said.

Brian McCluney and Justin Walker. via WESH

On Tuesday, Vlaun said that the search had covered more than 50,000 square miles and was still "100 percent a rescue operation," noting that the men were resourceful due to their line of work and McCluney's experience in the Navy.

Walker's wife, Natasha Walker, said the two men have been friends since college and they fish together whenever Walker travels to Florida, where he is from, to visit. "Their big thing is always fishing," she said. "That's their time together."

McCluney's brother, Kevin McCluney, told NBC News that both men are familiar with the area and boats. "If this had to happen to anybody, these are the right people to get through it," he said.

"I am very confident Brian and Justin will be found — it's just a matter of time," Kevin McCluney said. "My brother has excellent survival training from the Navy, he's been through two deployments and came back safe and sound so he'll be good to go here."

More than 20 agencies, including the Coast Guard, the Navy, U.S. Customs and Border Protection Air and Marine Operations, the Florida Fish and Wildlife Conservation agency, the Brevard County Sheriff's Office, along with more than 100 volunteers have joined in the search with crews on the water, in the air and on the shore.

On Monday alone, more than 135 volunteers, including dozens of firefighters, searched 5,000 square miles, according to the Jacksonville Fire and Rescue Department. The department urged the public to report any debris sightings to the Coast Guard and asked those who couldn't help in the search to donate to support efforts to find the two men.

“I’ve seen the incredible support the families of these two men are receiving on social media,” said Jacksonville Director of Air and Marine Operations Jesse Wozniak. “There are a lot of people working to find them and praying for their safety."

"Friends, family and Public safety pros are working hard," echoed Jacksonville Mayor Lenny Curry. "While they work, Pray. Prayer is powerful."