Pakistani activist Malala Yousafzai made a pledge during her trip to Nigeria on Sunday to help free the hundreds of Nigerian schoolgirls who remain missing after being kidnapped in April.

Yousafzai, who was shot in the head for defying the Taliban's rule prohibiting girls attending school, was at a meeting with some of schoolgirls' parents when she pledged to join the Bring Back Our Girls movement demanding their return, The Guardian reported.

"I can see those girls as my sisters...and I'm going to speak up for them until they are released," said Yousafzai, who turned 17 on Monday.

On the night of April 14, the Islamist militant group Boko Haram abducted nearly 300 girls from their boarding school in the Borno state village of Chibok. Dozens of girls managed to escape their captors, but some 200 remain missing and Nigeria's government and military has since faced international pressure to bring the girls home.

Yousafzai held a pre-birthday celebration on Sunday with some of the girls who escaped.

"I'm going to participate actively in [the] Bring Back Our Girls campaign to make sure that they return safely," Yousafzai said according to The Guardian.

When she was just 14, Yousafzai was shot by Taliban militants moments after she boarded a school bus in the Swat district. After recovering from two gunshot wounds to the head, the teen became a leader in the fight against the Taliban's crimes and a symbol for peace.

Now, Yousafzai has joined the fight to rescue the schoolgirls. But what was initially a global demand for justice has since died down to a small group of family members who hold daily protests in the Nigerian capital Abuja, The Guardian reported.

"We parents thank you all for standing with us all this while," Shettima Haruna, whose daughter was kidnapped, said according to The Guardian. "If not for your support, interest would have died down completely. The only reason this case is still receiving attention is through this group."

In the meantime, Nigeria's military knows the location where the girls are being held, but is hesitant to act out of fear of retaliation from the militants.