He said the US team, working with the Nigerian government, would do everything possible to free the girls.
Earlier, Nigerian President Goodluck Jonathan said he hoped "a turning point" had been reached in the fight against Islamist insurgents Boko Haram.
Nigeria has been criticised for its slow response to the kidnappings.
The schoolgirls were seized from their boarding school on the night of 14 April in the town of Chibok in north-eastern Borno state.
The Nigerian group's latest actions have attracted such unanimous international condemnation that few will want to be publicly associated with them for quite some time”
It is believed they are being held somewhere in the vast forested areas that stretch from near Chibok into neighbouring Cameroon.
"Our inter-agency team is hitting the ground in Nigeria now and they are going to be working in concert with President Goodluck Jonathan's government to do everything that we possibly can to return these girls to their families and their communities," Mr Kerry said.
"We are also going to do everything possible to counter the menace of Boko Haram."
On Wednesday, President Barack Obama said the team comprised personnel from military, law enforcement and other agencies.