Francois Hollande says they belong to the same family and were seized by a “known terrorist group based in Nigeria”.
The president added that the seven were probably taken to northern Nigeria.
He indicated that the Nigerian Islamist militant group Boko Haram may have been responsible.
“I see the hand of Boko Haram in that part of Cameroon, and that is worrying enough for us to mobilize,” Francois Hollande said.
He said everything possible was being done to rescue the family and warned other French nationals in northern Cameroon to avoid “exposing themselves”.
The family had been returning from a visit to Waza National Park when they were attacked by men on motorcycles, Cameroonian officials said.
The incidents come amid a French-led intervention against Islamist militants in Mali.
At least eight French nationals were already being held by Islamist groups in Africa.
Boko Haram has staged many attacks across northern Nigeria in recent years, targeting churches, government buildings and the security forces.
Another Islamist group- Ansaru – is also active in the region.
On Sunday, Ansaru claimed the abduction of seven foreign workers in Nigeria.
Italian, British, Greek and Lebanese workers are thought to be among those held after an attack on a construction project in Bauchi state.
Ansaru also says it is holding a French national, Francis Colump, who was seized in the northern state of Katsina.
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