Justin Walker and Brian McCluney left Port Canaveral -- 50 miles east of Orlando -- Friday morning in a 24-foot center console vessel to head toward the "8A" reef to fish, the Coast Guard said in a statement Saturday.
Family members notified officials when they didn't return by Friday evening.
The Coast Guard said reports of a similar boat 50 miles off Jacksonville turned out to be unrelated debris, Fox 30 noted.
As of Sunday, search crews had covered 4,800 square miles, the Coast Guard said in a Facebook post.
The search has been concentrated in the Gulf Stream area on water and air. Multiple agencies, as well as good Samaritans using their own boats, were participating.
Tampa Bay news outlet WFTS reported that Walker is employed as a master technician with the Fairfax, Va., fire department and McCluney works for the Jacksonville fire department, according to the International Association of Fire Fighters, which counts both men as members.