Caroline Mwatha, who is a senior official and a founder member of the Dandora Community Social Justice center, did not report to work on Wednesday last week.
Mwatha has been a leading crusader against extrajudicial killings in slum areas.
Her husband is set to jet in from Dubai today where he works.
It is said the mother of two had taken one of her children to school in the morning of the fateful day but did not return.
One of her colleagues James Omondi told Radio Jambo that Mwatha's phone went unanswered and then became unreachable.
By yesterday, hopes of her relatives and friends were alive as a search for her in the mortuaries in the city were fruitless.
Caroline’s father Stanislas Mbai said they had searched for her at Kenyatta National Hospital, Mama Lucy Hospital, Dandora hospitals and even city mortuaries to no avail.
“We are doing everything we can. We believe she is still alive because my son and her friends went to look at every mortuary, but she was not there,” Mbai told said at his Dandora home.
Buru Buru police officers have so far recorded statements from her neighbour and parents. The parents live a kilometre away from Caroline’s house. The police are today expected to get a report from Safaricom on her call logs.
There were anxious moments yesterday when members of the lobby were informed of a body found in Nairobi River. They all rushed to see the body, but it turned out it was a man’s.
Amnesty International yesterday urged the police to conduct speedy and thorough investigations on Caroline’s disappearance.