Boko Haram militants abducted 276 girls from their school in Chibok more than two years ago.
The Nobel Peace Prize winner writes to the parents of 219 Nigerian schoolgirls kidnapped by Boko Haram two years ago.
Two years on, Nigeria and its allies must not give up searching for the 219 teenagers still missing.
A report says half of the militant group's suicide attacks in Cameroon are carried out by children.
The abduction was larger than that of the Chibok girls but received little attention.
The girls have been missing since April 14, 2014, when they were abducted by Boko Haram.
The army has accused traders of "sustaining terrorism" by smuggling goods to the militant group.
Boko Haram kidnapped more than 200 schoolgirls in April 2014.
Almost two years after their abduction, the Bring Back Our Girls group is marching on President Buhari's house.
More than 200 girls remain missing despite Buhari's claim that Boko Haram had been "technically" defeated.
Hassan John is a Christian pastor in Jos, central Nigeria. Boko Haram wants him dead.
The Nigerian army have entered Sambisa Forest, thought to be Boko Haram's last stronghold.
Warplanes lead offensive into Sambisa forest, 100 km from village where Boko Haram abducted 200 girls last year.