"There will be no rest till the last girl, whether from Chibok and (or) Dapchi, is released," Buhari said in a statement, referring to the towns where the terror group has struck in the past four years.
The Nigerian leader spoke Wednesday while visiting the Government Girls Science Technical College in Dapchi, a town in Nigeria's Yobe state where Boko Haram abducted 110 schoolgirls in a February 19 raid. It marked his first trip there since last month's attack.
In April 2014, Boko Haram sparked international outrage when it kidnapped 276 girls from a boarding school in Chibok, a town in Borno state. More than 100 of these girls remain in captivity, and their whereabouts.
In Dapchi, Buhari met Wednesday with families of the missing girls, saying his administration has remained resolute in fighting terrorism and ensuring the students are returned safely.
"We have re-equipped our armed forces, security and intelligence services," Buhari said, adding that Nigeria's air force is maintaining aerial surveillance of the area.
Buhari said the government was investigating circumstances that led to the girls' abduction and warned that "any agency, person or group found to have been negligent or culpable" would be punished.
He said he is confident that all the missing girls will be rescued or released and returned safely to their families.
"The government, under my watch, will continue to maintain normalcy and ensure that incidents of this nature are stopped," Buhari said.
Bashir Manzo, who attended the meeting, told CNN that he and other parents are anxious but are patiently waiting for the girls' rescue. Manzo's daughter, Fatima, 16, is among the missing.
"We want our girls back, but we will give them the time they need to find them," says Manzo, who was elected head of a parents' association for the missing Dapchi schoolgirls.
The Nigerian leader last month called the abductions a "national disaster."
He has said Nigeria is working with international organizations and negotiators to ensure the girls go free unharmed.
"Our resolve (is) to negotiate for the unconditional release of the girls," Buhari said in a statement Wednesday.
"Doing so is safer ... and will not endanger the lives of our young girls who are in harm's way," he said.
The government last year freed five top Boko Haram commanders in exchange for the release of 82 of the Chibok schoolgirls.
Nigerian army spokesman John Agim told CNN last week that one of those freed commanders, Shuibu Moni, would be apprehended again after he taunted the military in a recent propaganda video from the militant Islamic group.