Malala Yousafzai,the Pakistani teenager shot in the head by the Taliban for championing the right of girls to education, has pledged on a visit to Nigeria to help free a group of more than 200 schoolgirls who have been held captive by Islamist militants Boko Haram since April.

The activist, who turns 17 on Monday, held an early birthday celebration with some of the girls who escaped the mass abduction in the north-eastern village of Chibok in April. “I can see those girls as my sisters… and I’m going to speak up for them until they are released,” she said during a meeting on Sundaywith some of the parents of the abducted children in the capital, Abuja. “I’m going to participate actively in [the] Bring Back Our Girls campaign to make sure that they return safely.” Later, standing beside four visibly delighted children from Chibok, she blew out the candles of a birthday cake.

Malala was shot shortly after boarding a school bus in 2009 by Taliban insurgents in Pakistan’s Swat district, an event that turned her into a global symbol of defiance against the militants. Similarly, the abduction of 300 secondary school girls has shone a global spotlight on the atrocities of Boko Haram, whose name means “western education is forbidden”.

A social media campaign, #bringbackourgirls, drew support from Angelina Jolie and Michelle Obama. But attention has since waned, and a small but determined group of relatives who hold daily rallies for the girls say they have been intimidated by the government, which has faced a barrage of negative publicity over its handling of the incident.

Meeting a group of parents of the abducted girls, Malala said: “Thank you for your great work and for such courage … you are really brave parents.” Some of the parents wiped away tears as she spoke.

Later, parents and four of the girls attended the daily rally in the centre of Abuja, sitting in silence as a crowd chanted. One supporter likened the rallies to a “long battle in which we have faced arrest, intimidation and distractions”.

“It’s great for Malala to come here and refocus attention on the issue. At the same time, that it took Malala coming to meet our president is an indictment on how Nigeria is handling this crisis,” said Toyin, a supporter in her 20s.

Shettima Haruna, whose daughter Margaret was abducted, stood up at the rally and addressed the crowd: “We parents thank you all for standing with us all this while. If not for your support, interest would have died down completely. The only reason this case is till receiving attention is through this group.”

Another Chibok resident explained why more of the mothers weren’t there: “Some of the women are so devastated by the events they can’t even cook any more.”

Boko Haram’s half-decade battle to impose an Islamic caliphate in Africa’s most populous nation has become increasingly bloody in the last year. Civilians have increasingly been targeted, and last year the insurgents burning dozens of schoolchildren alive in their dorms. Pakistan and Nigeria have some of the highest numbers of children out of school. In Nigeria, girls make up around two-thirds of the 10.5 million outside the school system.

According to Justin Forsyth of Save the Children, which is working in partnership with the Malala Fund, 50 million children living in conflict situations are denied their right to education. “In countries like Syria, South Sudan and Nigeria, schools are targeted in attacks and often used as military bases. Many of the children I’ve met have told me that one of their top priorities is to return to school,” he said.