Emiliano Sala was on board a plane that has gone missing while travelling from Nantes to Cardiff, the French Civil Aviation Authority has told AFP.
Argentine Sala, who was confirmed as Cardiff City's record signing on Saturday after opting to leave Ligue 1 Nantes, is said to have been one of two people on the aircraft that disappeared on Monday while crossing the English Channel.
An immediate search and rescue operation was launched in the area but was halted in the early hours of Tuesday due to worsening weather conditions. Local and French authorities resumed their efforts at 0800 local time.
Guernsey Police tweeted an update at 1145, saying: "So far over 1,000sq miles have been searched by a total of five aircraft and two lifeboats. It is being co-ordinated by the Joint Emergency Services Control Centre.
"There has been no trace of the aircraft. The search is continuing."
Club chairman Mehmet Dalman was quoted as saying in a statement on Tuesday: "We are very concerned by the latest news that a light aircraft lost contact over the Channel last night.
"We are awaiting confirmation before we can say anything further. We are very concerned for the safety of Emiliano Sala."
In a statement published on Facebook early on Tuesday, Guernsey Police said: "Guernsey Coastguard received an alert at 2023 from Jersey ATC, that a light aircraft had gone off their radar approximately 15 miles north of Guernsey, initiating a major search and rescue operation involving both St Peter Port and Alderney lifeboats. Air Search 1 and 2 HM Coastguard helicopters are also involved in the search.
"The PA 46 Malibu, a single turbine engine aircraft was on route from Nantes in France, to Cardiff in Wales, with two people on board when it was lost off radar as Jersey ATC was attempting to make contact.
"A search model was created on SARIS, based on the likely ditching position, and all search and rescue assets were tasked to the area.
"The search was terminated at 0200, with all search and rescue assets being stood down, due to strengthening winds, worsening sea conditions and reducing visibility. At this time no trace of the missing aircraft had been found.
"The aircraft departed Nantes at 1915 for Cardiff. The aircraft was flying at 5000 feet. The aircraft on passing Guernsey requested descent. Jersey ATC lost contact whilst it was flying at 2300 feet.
"Air Search 1 and a French rescue helicopter based in Cherbourg, resumed the search of the area at 0800."
Sala's father, Horacio, told Argentine media he was "desperate", according to L'Equipe.
His mother, Mercedes, said to C5N: "The plane is [owned by] the president of the Cardiff club. We were informed the plane had disappeared and that they were looking for it. We're in touch minute by minute."
Nantes president Waldemar Kita told CNews: "I'm not aware of anything. I just learned as you did about an hour and a half ago, from journalists, who told me there was a plane that left yesterday. I didn't even know he was in Nantes.
"I'm hopeful we'll find him again."
Sala, 28, joined the Bluebirds from Nantes on a three-and-a-half-year deal. He said his goodbyes to his team-mates at the Ligue 1 club on Monday.
It is reported that Nantes' Coupe de France match with Entente Sannois Saint-Gratien, scheduled for Wednesday, will be postponed.