One of the top trending topics on Twitter in Kenya is #FindCarolineMwatha
Ms Mwatha, who is a leading campaigner against extra-judicial killings by the police, has been missing for six days. She is a founding member of the Dandora Community Justice Centre (DCJC) which documents cases of extrajudicial killings in Dandora estate in the eastern part of the capital, Nairobi.
Kenya's rights group Missing Voices describes Ms Mwatha as "a gallant human rights defender".
It says her friends and family have reported to the police that she is missing but have also been going around hospitals and morgues looking for her.
Amnesty International has also joined the search:
Caroline is a founder member and a case worker of @DandoraJustice who has been missing for 6days now, we are still looking for her and we hope to find her safe and sound.@NationBreaking @JBoinnet@Shikohkihika @robi_chacha#FindCarolineMwatha