A teenager critically injured in a suspected hit-and-run near Wollongong in New South Wales posted a Facebook message saying she was approached by a stranger moments before the accident.

April's Facebook post moments before she was found critically injured on the road. ( Facebook )

April-Lee Gillen, 17, was found unconscious on Northcliffe Drive at Lake Heights, just south of Wollongong, about 1am (AEST) on Sunday.

She suffered life-threatening head injuries and remains in hospital in a critical but stable condition.

The teenager was found lying injured on the road soon after posting the following Facebook message:

"Phones on 1 percent walking from Warrawong to berks [Berkeley] and some Asian guy just stopped me telling me to come home with him cause it's safe and I need help wtf sos," it read.

Police say Ms Gillen's message is a vital part of their investigation.

Inspector Steve Worthington from Lake Illawarra Police says authorities are particularly keen to speak with the man mentioned in the post.

"That is certainly vital information our detectives are following up. But until we can speak to April herself, we need further information from the public," he said.

Inspector Worthington says police are still treating the incident as a suspected hit-and-run, but they have not ruled out other possibilities.

April-Lee Gillen posted a message on Facebook that her phone was about to die. ( Facebook )

"There's lots of speculation out there but not a lot of hard evidence," he said.

"The crime scene was examined thoroughly by our specialist crash investigation unit and detectives really need information from the community.

"We need the facts about what took place."

Witnesses in the neighbourhood told police they heard a loud noise just before the teenager was found on the road.

There are also reports that the incident was filmed by someone, but Inspector Worthington says he cannot comment on that at this stage.