Rescuers searched for survivors for the third straight day on Tuesday after the Cessna airplane disappeared in foul weather on Sunday.

U.S. businessman Michael Klein, together with his daughter and her friend, both aged 13 years old, were on the plane along with their Panamanian pilot, Klein's family said.

The airplane disappeared from radar on Sunday during a 45-minute flight between Islas Secas, in the Gulf of Chiriqui, and Volcan, a mountainous coffee-growing region, the government said.

Klein's family said that in addition to the reward, it would pay for rental of four-wheel drive vehicles as well as air plane and helicopter searches.

Poor weather, including fog and heavy rains, has forced rescue workers to intermittently suspend their search for the missing plane, the government said.