She met parents of the more than 200 girls who were kidnapped by the militant group Boko Haram from a school in the northeastern village of Chibok in April.
Boko Haram, inspired by the Taliban, say they are fighting to establish an Islamic state in religiously mixed Nigeria.
The group, whose name means "Western education is sinful", has killed thousands and abducted hundreds since launching an uprising in 2009.
Some of the parents broke down in tears as Malala, 17, who also met President Goodluck Jonathan, spoke at a hotel in the capital Abuja.
She said: "I can see those girls as my sisters and I'm going to speak up for them until they are released.
"I'm going to participate actively in the 'Bring back our girls' campaign, to make sure that they return safely and they continue their education."
The girls' abduction drew unprecedented international attention to the war in Nigeria's northeast and the growing security risk that Boko Haram poses to Nigeria, Africa's leading energy producer.
Mr Jonathan has pledged to save the girls.