Family and friends including his sister Sian Phillips gathered outside the Brazilian Embassy just after 8am on Wednesday carrying signs reading “Find Dom and Bruno”.
She told The Guardian: “He is a great writer and journalist, a caring man … And cares about the environment and loves Brazil.”
Asked if she believed her brother would be found, she said: “We all still have hope. We have hope.”
She added: “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.”
Meanwhile, legendary Brazilian footballer Pelé joined calls for authorities to investigate the pair’s disappearance.
Pelé, 81, retweeted a video made by Mr Phillips’s wife calling for an urgent search for the pair.
Mr Phillips, 57, has reported from Brazil for more than a decade and has been working on a book about preservation of the Amazon.
A suspect named as 41-year-old Amarildo da Costa de Oliveira, also known as Pelado, was arrested for allegedly carrying a firearm without a permit, a common practice in the region.
Police did not clarify why he was being treated as a suspect.
Four other people have been questioned since the investigation started but no arrests related to the disappearances have yet been made, according to authorities.