Christian Kath, 42, and his wife Misty Kath, 43, were flying with their teenage daughter Lily when their plane crashed into the Gulf of Mexico.
The family was living in St Petersburg in Florida but previously lived in Queensland.
The single-engine Piper Cherokee was reported overdue Saturday when it did not return to its origin airport.
Police Chief Charlie Thorpe told reporters on Monday recreational boaters found the body of a woman floating about four kilometres west of the Venice shore.
A young girl’s body was found in the wreckage of the aircraft.
All three victims were family members who had planned a dinner in Venice before returning to St Petersburg, Thorpe said.
It’s not yet clear what caused the plane to crash, he added.
It is understood the pilot was Christian Kath, who is still missing but believed to have died in the crash, according to the City of Venice.
“After consultation with the Coast Guard, the search area for the missing pilot in the Gulf has been expanded area-wise, but assets have been scaled back,” the city said on Twitter.
“Boaters from Sarasota Bay south to Gasparilla should be aware of the possibility of a body or small aircraft debris floating.”
Kath recently posted on Facebook that he was learning how to fly solo, completing his first trip on March 22.
The county sheriff’s office, the US Coast Guard, the Sarasota Police Department, Florida Fish and Wildlife Conservation Commission and the District 12 Medical Examiner’s Office and the National Transportation Safety Board were involved in the investigation.
The Department of Foreign Affairs and Trade has been contacted for comment.
– Reported with Associated Press