President Francois Hollande's office said after he spoke by telephone with Nigerian leader Goodluck Jonathan that Paris would dispatch a specialised team in the coming hours to Abuja to help find the girls.
With more than 4,000 troops operating between Mali to the west and Central African Republic to the east, Paris has a major interest in preventing Nigeria's security from deteriorating and has voiced concern Boko Haram could spread north into the Sahel.
Having ousted al Qaeda-linked militants from Mali last year, France is planning to redeploy its forces across West Africa this summer to target Islamist groups taking advantage of porous borders between southern Libya, northern Chad and Niger.
"The president expressed his desire to increase intelligence cooperation with Nigeria, involving all regional countries, so that this terrorist group can no longer carry out such acts," a statement on the telephone conversation said.
Earlier on Wednesday, Foreign Minister Laurent Fabius told lawmakers: "In the face of such ignominy, France must react. This crime cannot be left unpunished."
Around 10 experts from the external DGSE intelligence service with satellite observation knowledge would first be sent to join United States and British teams, official sources said.
Demanding an Islamic state, Boko Haram has been fighting in the northeast for the past five years. It attracted global attention last month with the abduction of girls taking exams in the village of Chibok, also in the south of Borno state.
FRENCH TARGETS
Underscoring how far Nigerian security forces are from protecting civilians in a region, the group launched an attack that killed at least 125 people, police said on Wednesday after gunmen rampaged through a town in the northeast, near the Cameroon border.
Hollande, during a February trip to Abuja, promised to help fight them, saying Nigeria's struggle was also that of France.
"This may be the catalyst the international community needs to fight Boko Haram," a French diplomat said.
French interests have already been targeted by Boko Haram.
Last November, the group kidnapped a French priest and held him for a month. Earlier last year, in mid-February, they snatched a French family of seven on holiday in northern Cameroon and held them for two months.
Hollande at the time denied a ransom had been paid for the family, but a confidential Nigerian government report seen by Reuters said Boko Haram was given the equivalent of $3.15 million by French and Cameroonian negotiators.
The kidnappings were among a series of attacks on French targets in West Africa since France launched a military intervention in Mali in January 2013 to oust al Qaeda Islamists who had forged links with Boko Haram.
Nigeria has complained that the far northern region of Cameroon is being used by Boko Haram militants to transport weapons and hide from a six-month military offensive against them. It has appealed to Cameroon to tighten border security.
Officials in Niger, where France has based surveillance drones, have also voiced concern about infiltration by Boko Haram across the country's southern border.
"We're already at the forefront of the fight against terrorists in the Sahel and with borders so easy to cross these groups are linked," the diplomat said. "We have knowledge in neighbouring countries that can help."
