Itai Dzamara, who was also a journalist, was kidnapped by five men as he left a barbershop near his home in Harare in 2015. He has not been seen since then.
In a statement, European Union and top US diplomats encouraged “the new administration to ensure that human rights violations are tackled decisively and transparently, to shed light on Mr Dzamara’s fate and to serve justice”.
“His disappearance remains a dark shadow on the new horizon for Zimbabwe,” they said on the anniversary of Dzamara’s abduction
He had led anti-government protests in a public park in the capital, overlooking parliament, vowing to not stop until Mugabe stepped down.
During one of the protests he was beaten by ruling ZANU-PF party members and left bleeding on a pavement.
– ‘A just Zimbabwe’ –
Dozens of activists gathered Friday in the same park where Dzamara used to stage he protests, demanding his return, “dead or alive”.
“We are drawing a line in the sand that never again shall we have abductions,” Dzamara’s young brother Patson said.
“Itai’s abduction was overseen by the ZANU-PF government… by the military intelligence,” he claimed.
“Enough is enough on abductions. Itai must be the last person to be abducted,” he said vowing to step up pressure on the new government of Emmerson Mnangagwa.
Clad in t-shirts emblazoned with portraits of the missing Dzamara and quotes from his speeches, the activists carried placards written #BringBackItai.
They recited prayers and chanted songs in honour of Dzamara under the close watch of riot police with water cannon.
A protestor and fellow activist Dirk Frey, described his compatriot as brave and courageous.
“He gave us the courage even when we were beaten, arrested and tortured. He wanted a free, fair and just Zimbabwe,” Frey said.
“We and our children deserve a just Zimbabwe. It will not be handed on a silver platter, we must fight for it.”
The government has denied involvement in Dzamara’s disappearance and has said it had no information on his fate.
The global rights watchdog Amnesty International called on authorities in Zimbabwe to scale up the search for Dzamara.
“People don’t just vanish into thin air. Someone out there knows what happened to Itai Dzamara,” said Deprose Muchena, the regional director for Amnesty in Southern Africa.
“The government must scale up Itai’s search. Impunity must not be allowed to thrive,” he said in a statement.
Mugabe who presided over Zimbabwe’s slide from a regional breadbasket to a perennial food importer, stepped down following a military intervention last November.