Mr Warner said police urged the driver to come forward.
Police would also like to speak to any witnesses who saw the incident or anyone with any information about the pedestrian or the whereabouts of the driver, he said.
The patient was yesterday still in Waikato Hospital, surrounded by loved ones, and was reported to be in a critical condition for most of the day. He was moved to a ward about 7pm after he was assessed as being in a stable condition, a hospital spokeswoman said.
Te Puke St John station manager Simon Campbell said St John staff were called to the incident about 9.30pm and took the 19-year-old to Tauranga Hospital. He was then transferred to Waikato Hospital.
St John spokeswoman Victoria Hawkins said three ambulances attended the incident following multiple calls.
"One said he had been hit by a car and another one said they had just come across him lying unconscious on the road."
Mr Warner could give away little about the police investigation.
"I don't want to go there because I'll let the person know that I'm looking for them, but we are doing quite a few things ... inquiries are ongoing is all I'm prepared to say."
Mr Warner could also not say what the young man had been doing on the road.
"We are still making inquiries in relation to it obviously - because he's in hospital, we haven't been able to talk to him."
Police had still to interview a number of witnesses, he said.
Wes Archer, who manages nearby Kiwi Corral Te Puke Backpackers Hostel, was unaware of any campers witnessing the incident and didn't realise anything had happened until he noticed some white dotted lines painted on the road yesterday morning.
Maketu and Te Puke fire brigades also attended the incident to provide lighting.
Maketu fire chief Shane Beech said the spot used to be problematic for traffic congestion, but he was unaware of any pedestrians having ever been struck there previously.
Anyone with any information should call police on 577 4300 or the Crimestoppers hotline anonymously on 0800 555 111.
Additional reporting NZME