He told RNZ today investigators had received information that potentially confirmed a sighting of Johnson in the central North Island.
“We do want to hear from anyone with information that could be beneficial,” he said.
“A lot of the time is spent filtering through and sorting what may be a priority and what may be historic and not of interest to our timeline.
“Certainly, we’ve appreciated the public outreach and there are a number of lines of inquiry that we’re looking into.”
Johnson’s mother was arriving in New Zealand from Seattle this morning.
Gillam said her arrival in Palmerston North would be key, allowing her to speak with police and staff at Massey.
No search parties were in place at this stage, as more specific information would be needed, although aerial searches were under consideration.
Johnson was last seen in the Takaro area of Palmerston North.
Gillam said his disappearance was “really traumatising” for his family, who were distraught.
His company had three investigators working on the matter fulltime.
On Tuesday, Gillam said it was out of character for Johnson not to have contact with his family for such a period of time.
Johnson was known to make off-the-cuff trips to Auckland.
Police have said they received a missing person report on June 9.
“Police have made a number of various area inquiries in possible locations of interest in the Palmerston North area,” a spokeswoman said today.
“We would encourage William, or anyone who knows his whereabouts, to get in touch with police to confirm he is safe.”
Johnson drove a 2013 silver Mazda 6, registration MJK496, which was also missing and could provide leads to his whereabouts, Gillam said.
He can be contacted on 027 299 7603.
– RNZ
