The mass kidnapping last month by militant group Boko Haram, which is fighting for an Islamic state in north-east Nigeria, triggered an international outcry and protests in Nigeria, piling pressure on the government to get the girls back.
Anger mounted after locals on Tuesday said another eight girls had been seized by suspected members of the group. Police listed six phone numbers in their statement and urged Nigerians to call in with "credible information".
Boko Haram leader Abubakar Shekau has threatened in a video to sell the girls, who were abducted on April 14 from a secondary school in the village of Chibok.
Suspected Boko Haram gunmen kidnapped eight more girls from a village near one of the Islamists' strongholds in north-eastern Nigeria on Monday night.
The kidnappings, and other attacks by Boko Haram, have overshadowed Nigeria's hosting of the World Economic Forum, which started yesterday. Nigerian officials had hoped the event would draw attention to the potential of Africa's biggest economy as an investment destination.
Last month's kidnapping occurred on the day a bomb blast, also claimed by Boko Haram, killed 75 people on the outskirts of Abuja, the first attack on the capital in two years. Another bomb in roughly the same place killed 19 people last week.
Nigerian President Goodluck Jonathan welcomed an offer from the United States to send a team to Nigeria to support the government's efforts to find the girls.