A $19 million luxury yacht deal brokered by Representative George Santos between two of his wealthy donors has captured the attention of federal and state authorities investigating the congressman’s campaign finances and personal business dealings.

The sale, which has not been previously reported, is one of about a dozen leads being pursued by the F.B.I., the U.S. attorney’s office in Brooklyn and the Nassau County district attorney’s office, people familiar with the investigation said.

Prosecutors and F.B.I. agents have sought in recent weeks to question the new owner of the 141-foot superyacht — Raymond Tantillo, a Long Island auto dealer — about the boat and his dealings with Mr. Santos, including his campaign fund-raising efforts.