The activists were forcibly taken away to an unknown location after a late-night "raid" yesterday, they said.
Those picked up by the authorities include an educationaist and rights activist, and a writer.
The two were not part of any any nationalist or political party and worked to spread education and provisions of basic amenities in rural areas, their families told reporters.
The area Senior Superintendent of Police said they had no knowledge about the "missing" activists.
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On August 5, some family members of the separatist leader of the banned Jeay Sindh Muttahida Mahaz, Shafi Burfat, were picked up from their residences.
Two days before that, Punhal Sario, the leader of the recently formed Voice for Missing Persons of Sindh, was reported missing from Hyderabad. His family members claim a dozen persons in police uniforms forcibly took him away.
Civil society organisations have taken out protest rallies in various cities agsint the increasing incidents of forced disappearances of rights activists, journalists and writers.