US President Barack Obama described the kidnapping of the girls as "heartbreaking" and "outrageous", soon after residents said the group had seized eight more girls, aged between 12 and 15, again in the embattled northeast.
Obama urged global action against Boko Haram and confirmed Nigerian leaders had accepted an offer to deploy US personnel there.
The first group of girls was taken three weeks ago, and concerns have been mounting about their fate after Boko Haram chief Abubakar Shekau claimed responsibility in a video, saying his group was holding the schoolgirls as "slaves" and threatening to "sell them in the market".
Shekau criticised the female students for being taught "western education", which the Islamic group is avidly against. He also warned that his group planned to attack more schools and abduct more girls.
Speaking to US broadcaster ABC, Obama said: "It's a heartbreaking situation, outrageous situation."
"This may be the event that helps to mobilise the entire international community to finally do something against this horrendous organisation that's perpetrated such a terrible crime," he added.
The team sent to Nigeria consists of "military, law enforcement, and other agencies", Obama said, and will work to "identify where in fact these girls might be and provide them help".
He denounced Boko Haram as "one of the worst regional or local terrorist organisations".
US officials have voiced fears that the girls, aged between 16 and 18, have already been smuggled into neighbouring countries, such as Chad and Cameroon. The governments of both denied the girls were in their countries, AFP reported.
Their fate has sparked global outrage and may constitute a crime against humanity according to the UN.
Parents of those taken said Shekau's video had made an already horrifying situation even worse.