Police said his family was aware of the development.
Insp Andy Wills said: “We are asking the public to help us with this by avoiding the search area.
“In particular, any activity on the water could significantly disrupt the search operation and put you and members of the emergency services at risk.”
He added: “We would also like to remind members of the public that drone flights are prohibited in the area while searches are ongoing.”
“All of the search activity is being directed by accredited police search advisers, who are defining search areas in consultation with colleagues including HM Coastguard.
“The public should expect to see focussed search activity around the River Taw,” he said.