The kidnappings have dominated news and political discussions in recent weeks, with at least six young men disappearing over the Christmas holidays.
At least two were taken after posting AI-generated images of President William Ruto in a coffin.
Among the four released on Monday was 24-year-old college student Billy Mwangi, found in northeastern Embu town “looking frail”, according to the Daily Nation newspaper.
His father, Gerald Mwangi, told Citizen TV his son was “well”, but would wait to ask about his ordeal.
The Kenya national commission on human rights has recorded 82 abduction cases since major youth-led protests broke out in June last year, with 29 still missing.
Police did not respond to AFP’s request for comment on Monday. They have previously denied involvement in abductions but have shown little sign of investigating the disappearances.
Rights groups blame a shadowy unit drawn from intelligence and counter-terrorism agencies.
“At this stage, it is definitely clear that the government was aware of the abductions at the highest level,” Irungu Houghton, director of Amnesty International Kenya, told AFP.
He said Monday’s releases were likely designed to undermine a court case brought against the government and police.
“They would have to go through a court process explaining why these people have not been released and is there a policy on enforced disappearances… That would have been very damaging,” said Houghton.
Ruto has successfully coopted the opposition, bringing parties into the government, but several key figures have voiced concern and anger over the abductions in recent days.
The tough police response, which saw at least 60 people killed during the initial protests, has dampened unrest in recent months.
A planned protest against the abductions on Monday drew scant participation.
But, Houghton said the government’s tactics were bound to backfire.
“The more the government behaves unlawfully and the more violently it behaves, the more anger it produces and the more reason people have to go to the streets,” he said.
The anti-government demonstrations last year were sparked by proposed tax hikes, triggering the worst crisis since Ruto took power in 2022.