Hundreds attended the ceremony in the southern city of Karachi, officials said.
Pakistan began a nationwide day of mourning over the killings of the members of the Ismaili community, with flags at half-mast at official buildings.
Markets were deserted and educational institutions were closed in Karachi and most parts of the southern province of Sindh, police official Najib Khan said.
At least six gunmen intercepted the bus carrying members of the Ismaili community in the port city on Tuesday. They barged into the vehicle and opened fire, Sindh province Information Minister Sharjeel Memon said.
A Taliban splinter group now affiliated with Islamic State militants claimed responsibility, reinforcing fears about Middle-Eastern jihadists' growing influence in Pakistan and Afghanistan.
Officials found a pamphlet at the site, carrying a warning by Islamic State, Khan said.
Violence has declined in Pakistan after security forces launched an offensive against Islamist militants linked with al-Qaeda in June last year.
But the increasing influence of Islamic State has added a new dimension to the complex network of conflicts in the country.