The sister of a British journalist missing in the Amazon has said she still has hope he will be found. Sian Phillips was joined by supporters at a vigil for her brother Dom Phillips, who has worked as a freelance correspondent for the Guardian, and the Brazilian Indigenous affairs official Bruno Araujo Pereira outside the Brazilian embassy in central London on Thursday. The two men vanished from a remote part of the rainforest more than three days ago, having reportedly last been seen early on Sunday in the São Rafael community. Some people held red roses while others clasped red and black posters that read “Find Dom and Bruno” and featured images of the missing pair’s faces, as they stood in silence in a line outside the entrance of the embassy from 8am. In a statement to the press, Sian Phillips, with her partner, Paul Sherwood, and twin brother, Gareth Phillips, by her side, said: “We had to come this morning, to ask the question: where is Dom Phillips? Where is Bruno Pereira? “And we are also here for my brother’s wife, Alessandra Sampaio. We are here with my brother’s nieces and sister-in-law too. “We are here because Dom is missing, he is lost doing the important job of investigative journalism. We are here to make the point that why did it take so long for them to start the search for my brother and for Bruno. “We want the search to carry on.” She spoke about how her brother was a “great writer and journalist, a caring man … and cares about the environment and loves Brazil” and that the whole family loved him. When asked about the chances of her brother being found, she added: “We all still have hope. We have hope.” In Atalaia do Norte, the isolated Amazon town where Phillips and Pereira spent their last night before heading into the Javari reserve, locals voiced shock and anger at their disappearances. “I still can’t believe it,“ said Marivalda Rabelo Laranhaga, the receptionist at the hotel where they stayed before starting their journey last Thursday afternoon. “He seemed such a polite and kind person … a journalist who was truly dedicated to his work,” Laranhaga, 31, added of Phillips, as Indigenous rescue workers prepared to head back out onto the river to continue their search. Meanwhile, O Globo newspaper reported claims that a significant suspect in the case had been seen loading a shotgun and leaving Atalaia with four other people on a powerful motorboat after Phillips and Pereira visited the town. Amarildo da Costa de Oliveira, 41, also known as Pelado, was arrested on Wednesday for allegedly carrying a firearm without a permit, a common practice in the region. At the vigil in London, Louisa Casson, the head of forests at Greenpeace UK, explained the meaning of the red roses. “We wanted something that conveys the love and admiration everyone here has for Dom and Bruno and for their work and amplifying the images already on social media with this clear message of find Dom and Bruno,” she said. At 9.30am a letter was given to the Brazilian ambassador from Greenpeace UK’s executive director, Pat Venditti, and Phillips’s family. Casson added that the letter presented “an urgent call on the Brazilian government to dedicate all necessary local and federal resources to the search mission for Bruno and Dom”. A Guardian editorial has called on authorities to scale up the so-far lacklustre response. “The government is highly unlikely to change course without international pressure,” it says. “That must first be brought to bear to produce an adequate response to this disappearance.”