The wife of the British journalist who has vanished in a remote corner of the Amazon with a celebrated Indigenous expert has issued an emotional plea for Brazilian authorities to work harder to find “the love of my life”. “I want to make an appeal to the federal government and the relevant organs to intensify their search efforts, because we still have some hope of finding them,” Alessandra Sampaio, the wife of longtime Guardian contributor Dom Phillips, said in a tearful video message. “Even if I don’t find the love of my life alive, they must be found, please – intensify the search,” Sampaio implored, breaking down as she spoke. Phillips, 57, was last seen on Sunday morning travelling by boat through the remote Javari region with an Indigenous advocate, Bruno Araújo Pereira. Days earlier, Pereira, who has spent years defending the region’s isolated tribes for Brazil’s Indigenous protection agency, reportedly received a written threat stemming from his opposition to illegal fishing gangs plundering the Javari’s rivers. “We know who you are, and we’ll find you to settle the score,” it warned, according to the newspaper O Globo. The pair were also threatened on Saturday, when a group of armed men brandished firearms at a patrol by members of the Univaja Indigenous association, according to the association’s president Paulo Marubo. Phillips photographed the men at the time, Marubo told the Associated Press. Brazilian police on Tuesday opened a criminal investigation into the men’s disappearance. Forty-eight hours after the two men were last seen heading towards the river town of Atalaia do Norte by speedboat, Phillips’s sister, Sian, said she was trying to stay positive despite the lack of news. She urged the international community to pressure Brazil to do more to find a man she called “a bright star” whose work illuminated the devastation of the world’s largest tropical rainforest. “Time is crucial, because we know there are situations where they could be abducted – but there’s also situations where they had a mechanical fault and they’re stuck and they have short supplies,” Sian Phillips said amid growing concern authorities had deployed insufficient resources. “So it’s crucial that [Brazilian authorities] are searching with all the equipment and local knowledge and resources that the army has,” Phillips added from her home in Lancaster. Late on Monday, Brazil’s navy said seven of its officials were involved in the search, while the army said members of a jungle infantry division had been sent to the men’s last known location by speedboat. Earlier in the day, the army had faced criticism after announcing that it had yet to deploy since orders had not been sent by the defence ministry in the capital, Brasília. Only on Tuesday morning is a helicopter believed to have joined the mission. Official photographs of the army deployment, showing a single vessel, did not point to a massive operation given the impressive military resources available in the Amazon region. Sian Phillips’s partner, Paul Sherwood, said: “We think it is evident that there is not a wholehearted response to this, and we want them to look as actively as they can because that is the only hope we’ve got.” Pereira’s partner, Beatriz de Almeida Matos, told the Folha de São Paulo newspaper: “I have a three-year-old son and one who is two. All I can think about right now is that he comes up safe, for the sake of the boys.” In a letter to the Guardian, Brazil’s ambassador to the UK, Fred Arruda, said he had contacted the federal police, army and navy and been reassured “they were sparing no effort in their search and rescue operation”. Brazil’s foreign ministry expressed “great concern” over the disappearances and said the federal police were doing everything possible to find the men as soon as possible. “The federal police have conducted repeated incursions, with support from the navy,” it said on Tuesday. “If the disappearance turns out to have been the result of criminal activity, all measures will be taken to bring the perpetrators to justice.” Sian Phillips called on the UK and US governments to lobby Brazil’s president, Jair Bolsonaro, who is due to meet his US counterpart, Joe Biden, at this week’s Summit of the Americas in Los Angeles, to do more. “He’s not going to do anything without having pressure put on him,” Phillips said of the Brazilian leader, whose presidency has overseen soaring deforestation and the dismantling of environmental protection agencies and laws. In his first official comments on the disappearance, Bolsonaro criticised what he called an inadvisable “adventure”. “Quite frankly, two people in just one boat, in that kind of region, absolutely wild, is an adventure that isn’t recommendable for anyone. Anything might happen. It could have been an accident. They could have been executed,” he added, prompting immediate outrage. In a letter to the British foreign minister, Liz Truss, the environmental group Greenpeace urged her “to use all diplomatic channels to urgently communicate to the Brazilian government the importance of mobilising all necessary federal and local resources to find the missing pair”. David Lammy the British shadow foreign secretary said: “I urge the Brazilian authorities to do all they can to find them as soon as possible and for the foreign office to use all the diplomatic channel at its disposal.” Friends and relatives of the missing journalist, who was born in Bebington, near Liverpool, described him as a caring and intrepid reporter who saw it as his mission to expose the environmental crisis playing out in the Amazon – and seek possible solutions. When he disappeared, Phillips was gathering material for a book about conservation, which had also seen him report from Costa Rica. “He wanted … to make it a mainstream book so that it alerted everybody to the problems with the destruction of the Amazon,” his sister said, before adding: “Dom is a bright star leading the lights of the world to this area – to spotlight this area right now.” She said she last heard from her brother last Wednesday as he set off for the rainforest from his home in Salvador, where he lives with his wife. “He sent us a picture of the Amazon with a rainbow over it from the plane,” she said.