The airline offered its condolences to the families of the passengers, making clear it did not expect to find survivors.
At least 60 of those on board were French, roughly 60 were Brazilians and two were Slovaks, their countries said.
Air France said the Airbus flew into stormy weather four hours after take-off from Brazil and soon afterwards sent an automatic message reporting electrical faults.
A company spokesman said several of the plane's mechanisms had malfunctioned.
"It is probably a combination of circumstances that could have led to the crash," he said, adding that the airliner might have been hit by lightning.
Aviation experts said lightning strikes on planes were common and were not enough alone to explain a disaster.
The Brazilian air force said the plane was far out over the the sea when it went missing.
Military planes took off from the island of Fernando de Noronha off Brazil's northeast coast to look for it and the Brazilian navy sent three ships to help in the search.
France sent one of its air force planes from west Africa.
Flight AF 447 left Rio de Janeiro on Sunday at 7 p.m. (2200 GMT) and had been expected to land at Paris's Roissy Charles de Gaulle airport on Monday at 11:15 a.m. (0915 GMT).
Storm Patch
"It is a zone in the tropics where you can have particularly deep thunder clouds," said Barry Gromett, a meteorologist at the London Weather Centre.
The carrier said 216 passengers were on board, including seven children and one baby, as well as 12 crew members.
The passenger list was not released, but French tyre company Michelin said the head of its Latin American operations, Luis Roberto Anastacio, had been on the flight.
Tearful relatives and friends were led away by airport staff after they arrived at Roissy expecting to greet the passengers.
About 20 relatives of passengers also arrived at Rio's Galeao airport on Monday morning seeking information.
Bernardo Souza, whose brother and sister-in-law were on the flight, complained he had received no details from Air France.
"I had to come to the airport, but when I arrived I just found an empty counter," he said.
Senior French government minister Jean-Louis Borloo ruled out the possibility of a hijacking.
If no survivors are found it will be the worst loss of life involving an Air France plane in the firm's 75-year history.
The plane was an Airbus 330-200 powered with General Electric engines. If the plane is confirmed to have crashed, it would be the first time an A330 has been lost during an operational airline flight.
Air France said the plane had 18,870 flight hours on the clock and went into service in April 2005. It last underwent maintenance in a hangar in April this year.
The last major incident involving an Air France plane was in July 2000 when one of its Concorde supersonic airliners crashed just after taking off from Paris, bound for New York.
All 109 people on board were killed along with at least four on the ground.
