Nigeria's president Muhammadu Buhari has invited the UN to lead talks with Boko Haram about a possible swap that would see the girls freed.
Boko Haram has kidnapped thousands of people but the mass abduction of 276 schoolgirls in April 2014 incited outrage around the world and brought international condemnation of Nigeria's home-grown Islamic extremist group.
Dozens of the girls have escaped, but 217 remain missing.
Mr Buhari's request for UN help is a "show of commitment" made to secretary general Ban Ki-moon, said a statement from presidential adviser Femi Adesina.
Mr Buhari told Mr Ban that his government is "willing to bend over backwards" to win the girls' freedom but finding credible Boko Haram leaders for the negotiations has been difficult, especially because of the current leadership struggle among the militants.
It's believed deals have been struck in the past but have ended up fruitless because other terrorists block the release of the girls.
Senior Boko Haram leader Abubakar Shekau posted a video in August showing about 50 Chibok girls and offering a prisoner swap.
An unidentified fighter in the video suggests the government deal with a journalist trusted by the militants. That was an apparent reference to Dubai-based Nigerian journalist Ahmad Salkida, who was subsequently detained by Nigerian intelligence agents, and then released.
He was accused of knowing the whereabouts of the girls - which he denied.
Last week, information minister Lai Mohammed said the government had nearly secured the girls' release three times but negotiations collapsed.
Most girls kidnapped by Boko Haram have been forced to marry fighters and are pregnant or have babies, according to some of the thousands freed in the past year as the military has recaptured territory.
