Tens of thousands of Argentines have demonstrated across the country, demanding answers one month after the disappearance of an indigenous rights activist.

On Friday, protesters held photos of Santiago Maldonado who was last seen when border police evicted a group of indigenous Mapuche from lands in Patagonia owned by Italian clothing company Benetton.

Demonstrators gathered at the Plaza de Mayo square in front of the presidential palace in Buenos Aires asking their government find the 28-year-old alive.

Maldonado's disappearance has hit a raw nerve in Argentina, where human rights groups estimate that about 30,000 people died or were forcibly disappeared during the 1976-1983 military dictatorship.

Maldonado's family says border police detained him when he and others were blocking a road in Chubut province, in the southern region of Patagonia. Maldonado and other protesters were demanding the release of a jailed Mapuche leader wanted by Chile.

Al Jazeera's Teresa Bo, reporting from Buenos Aires, said that those present at Friday's protest were calling Maldonado's disappearance a "forced disappearance".

"There are witnesses that have said that he was taken alive and that's why they [thousands of protesters] are here today," Bo said.

READ MORE: Argentina's indigenous Mapuche fight for ancestral lands

Bo added that the government is investigating Maldonado's disappearance, saying that "it's in our best interest" to do so.

The government has raided the border patrol that was responsible for last month's operation in Patagonia, but has not found any information regarding Maldonado's whereabouts.

Amnesty International and Human Rights Watch, as well as the United Nations, have said the activist's disappearance requires urgent action from Argentine President Mauricio Macri.

Online, #UnMesSinSantiago ("One Month Without Santiago") trended in Argentina on Friday, with many sharing photos from the marches and demanding Maldonado's return.