Reports said the passengers were taken from a convoy of buses heading from Balochistan Province to central Punjab Province late on August 5.
The gunmen reportedly wore the uniform of Pakistani security forces.
No one has claimed responsibility, but the attack appears to have targeted Punjabis who work in Balochistan.
Security forces who provide protection to buses traveling through Balochistan chased the gunmen, but lost them after the gunmen reportedly fired a rocket, killing one security officer.
Balochistan is home to separatists fighting for political autonomy and a greater share of the profits from region's mineral resources.
It has also seen sectarian violence between Pakistan's majority Sunni Muslims and Shi'ites.