Premier League footballer Emiliano Sala was on a light aircraft which went missing over the Channel Islands.
The £15m Argentine striker, 28, was one of two people on board the Piper Malibu which lost contact off Alderney in the Channel Islands on Monday night.
Cardiff City, which signed Sala from French club Nantes in a record deal on Saturday said it was “very shocked”.
Guernsey Police said there was “no trace” of the Cardiff-bound flight and has suspended the search for the night.
“We have found no signs of those on board,” the force tweeted.
“If they did land on the water, the chances of survival are at this stage, unfortunately, slim.”
Hundreds of fans gathered in Place Royale, Nantes and laying tulips at a fountain.
The gesture is a tribute to Sala and the pilot on board the flight.
Sala’s father, Horacio, told Argentine TV channel C5N, he heard the news from a friend.
“I didn’t know anything. I couldn’t believe it,” he said. “I’m desperate. I hope everything goes well.”
Meanwhile, John Fitzgerald, chief officer of the Channel Islands Air Search, said the probability of finding anyone alive from the missing aircraft was “reducing very rapidly”.
“I think with the sea temperatures and the sea conditions the chances of finding anybody alive are reducing all the time,” he said.
“The sea temperatures are very, very cold and just sap the core temperature of anybody in the water very, very quickly.”
The plane left Nantes in north west France at 19:15 and had been flying at 5,000ft when it contacted Jersey air traffic control requesting descent, Guernsey Police said.
The plane lost contact while at 2,300ft and disappeared off radar near the Casquets lighthouse, infamous among mariners as the site of many shipwrecks, eight miles (13km) north-west of Alderney.
The force added UK authorities have been calling airfields on the south coast to see if it landed there but there had been no confirmations and a decision about an overnight search would be made at sunset.
A spokesman for the French Civil Aviation Authority said the Piper PA 46 Malibu aircraft was French but had not been registered in France.
“We can confirm Emiliano Sala was on board,” he said.
“This morning, the French research started with one French national navy ship and one aircraft. The investigation will determine which authority will take the lead on the research.”