The winner of the Oscar for best actress, Frances McDormand, has spoken in support of activists seeking justice over the Grenfell Tower fire, who used her film Three Billboards Outside Ebbing, Missouri as inspiration for a publicity campaign.

Billboards were driven through central London last month saying “71 dead”, “And still no arrests?”, “How Come?”

The Justice 4 Grenfell campaigners took inspiration from the central theme of the film, in which McDormand’s character uses the same medium to call attention to the unsolved rape and murder of her daughter.

“Billboards still work, so I think that it’s really exciting,” said the American actor after accepting her award, praising “the idea that activists are taking that kind of statement and putting it out there”.

“It started actually with the Grenfell Tower fire investigation, then it leapfrogged to [the] Miami gun control situation, it was outside the UN ... That’s the kind of power that an image can have and that’s what we’re making, we’re making powerful images.”

Frances McDormand, left with her best actress award, with Jodie Foster and Jennifer Lawrence at the Oscars. Photograph: Matt Petit/Ampas/Getty Images

McDormand followed Stormzy in using a public platform to highlight the Justice 4 Grenfell campaign. The British grime artist demanded answers from the prime minister, Theresa May, over the fire during his performance at the Brit awards.

Moyra Samuels, one of the people behind the Grenfell billboards, was quoted by the BBC as saying: “It’s not just politicians who are taking note of what happened. We are being effective at raising the issues on a worldwide stage.”

Announcing the launch of the billboard campaign, the Justice 4 Grenfell activists said: “Eight months on from the tragedy of the Grenfell Tower, the issue is being ignored. 71 people died in the Grenfell Tower. And still no arrests.

“And still 297 flammable towers. And still hundreds of survivors are homeless. And still they are not represented on the inquiry. And still there is no justice.

“These three billboards are here to keep this tragedy in the national conscience, to make our voices heard. And our voices call for change to a system that kills. And our voices demand justice for Grenfell.”