According to BBC, his predecessor, Goodluck Jonathan, declined to meet the Bring Back Our Girls activists.
Mr Buhari promised the group that troops for a regional force to fight the militants would be in place by the end of July.
The kidnap of the girls from a school in Chibok sparked global outrage.
The mass abduction sparked one of the biggest social media campaigns of 2014, with the Twitter hashtag #BringBackOurGirls being used more than five million times.
Boko Haram has stepped up attacks since Mr Buhari took office in May vowing to tackle the insurgency "head on". BBC reports.
In the last week, more than 220 people have been killed in suspected militant attacks.