Sala, signed on Saturday from the French club Nantes for 17 million euros, was flying to Cardiff aboard a small plane that went off radars around 20 kilometres north of Guernsey on Monday night.
French civil aviation authorities confirmed that the 28-year-old Argentine was on board the plane with another passenger.
A statement from police on the island of Guernsey said the pilot had requested to lower his altitude shortly before air traffic control in neighbouring Jersey lost contact with the plane.
Two helicopters, two planes and a lifeboat joined renewed efforts on Tuesday to find the single-propeller plane.
"So far over 1,000 square miles have been searched by a total of five aircraft and two lifeboats," Guernsey police said on Tuesday. "There has been no trace of the aircraft. The search is continuing."
Sala, who had been at Nantes since 2015, had scored 13 goals in all competitions this season. He signed a three-and-a-half-year contract with Cardiff subject to receiving international clearance.
Neither club has commented on the disappearance. Nantes have had their French Cup match against third division Entente SSG on Wednesday postponed.