The chief executive of 2degrees and his wife were onboard the aircraft that plunged into the sea near Waikato on Saturday with the mobile phone company saying it's unlikely they survived.
Eric and Kathy Hertz have been missing since the twin-engined aircraft disappeared off the radar at 12.20pm near Raglan.
Rescuers called off a search for the pair on Saturday evening but will resume at first light on Sunday.
Eric and Kathy Hertz were travelling from Ardmore to Timaru when the plane's engine failed and lost contact with Airways New Zealand.
Oil and the wreckage was located 20 kilometres from the entrance to Kawhia Harbour, near Waikato on the west coast of the North Island.
A statement on 2degrees' website says the pair are unlikely to have survived.
Rescue Coordination Centre spokesperson Steve Rendle says they would have been found by now, if they had survived the crash.
He says where the plane went down has been searched without success by a helicopter, an aircraft and a coastguard vessel.
"Intensively searched that area, unfortunately there has been no sign of the two people that have been on board, we've handed the matter to the police."
2degrees says its focus now is on supporting the couple's daughter and providing assistance to their family.