Voice of Baluch Missing Persons chief Mama Qadeer made the allegation as he led dozens of protesters, including relatives of the "missing persons" into Karachi after a 27-day march from Quetta, the capital of Balochistan.
He said the government did not appear to be sincere about the missing persons or the plight of their families.
"We have come to Karachi to set up a hunger strike and protest camp to draw the attention of authorities and media toward this grave problem in our province," he said.
Qadeer said the protesters had started their march on October 27 from Quetta Press Club. "Most of these women and children have tears in their eyes and are carrying the pictures of their beloved who have gone missing," he said.
Baloch groups have claimed that scores of men have been detained without charge by security and intelligence agencies in recent years. Balochistan has been hit hard by a campaign by nationalist groups demanding greater autonomy and a say in the exploitation of the province's abundant natural resources.