Teenage victim posted Facebook message

A teenager posted a chilling message on Facebook just before she was found lying on a street in NSW's Illawarra region with critical head injuries.

"Phone's on 1 per cent 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," April-Lee Gillen posted online about 1am on Sunday.

Minutes later the 17-year-old was found unconscious on Northcliffe Drive in Lake Heights, south of Wollongong.

Ms Gillen suffered serious head injuries and remains in a critical but stable condition in intensive care at Wollongong Hospital.

Police initially treated the incident as a hit-and-run, with neighbours reporting hearing a loud bang around the time Ms Gillen was hurt.

However, since the Facebook message came to light detectives have broadened the enquiry and are now investigating whether the teenager was attacked.

"That's certainly vital information and our detectives are following it up," Inspector Steve Worthington said of the social media post.

Ms Gillen is still too sick to be interviewed by police who say someone in the community knows what happened to her.

"We're looking for a vehicle and we'd like to identify who she may have spoken to," Insp Worthington added.

"We're keeping an open mind.

"But until we speak to April herself we need to obtain some information from the public about it."