The search for missing teenage hiker Lily Hooper is becoming increasingly difficult as deteriorating weather moves across the rugged NSW Southern Highlands.

The 18-year-old experienced bushwalker left her home on Burragorang Rd in Oakdale about 8am on Wednesday to go hiking in Nattai National Park.

She had been texting her family about the hike, but when she failed to return home that night, they reported her missing.

Her vehicle was later found at the beginning of the Bonnum Pic walking trail along Wanganderry Rd.

NSW Police confirmed the search had continued on Sunday, with police concentrating their efforts on a specific trail in Nattai National Park.

The search remains complex, however, with numerous side trails branching through steep and heavily vegetated terrain as crews continue looking for any sign of the teenager.

“The terrain out there is extremely rugged,” Detective Inspector Benjamin Carey said in a press conference on Saturday afternoon, noting the terrain has made it “very challenging” for search attempts.

Further complicating matters, Carey said the weather was becoming “more and more inclement” over the search area.

Police are factoring the worsening conditions into the operation, with crews working urgently to find Lily before the weather deteriorates further.

The teenager’s disappearance has triggered a major multi-agency operation involving police, emergency services, specialist search teams, volunteers and members of Lily’s family.

Among those involved are the SES, RFS, NSW Police Rescue, the Mounted Unit, and the Dog Unit, with crews continuing to comb the national park.

Hooper’s family and friends have remained closely involved in the search as crews continue working across the national park.

“She has a lot of friends and a lot of support,” Carey said.

“They’re obviously very distraught and we’re doing everything we can to support them.”

Police are also still working to establish exactly what Lily had with her when she began the hike, including what equipment or supplies she may have been carrying.

The length of time Lily has now been missing, combined with the rugged landscape and worsening weather, has heightened concern for her welfare.

Carey confirmed police remain “hopeful” she will be found alive.

“We’re still hopeful that she’s alive and we’re going to continue with our multi-agency focus on searching the area as thoroughly as we can and delivering the outcome for this family,” Carey said.

Police have also renewed their appeal for information from anyone who may have seen Lily, spoken to her or been in the area around the time she disappeared.

Lily is described as being of Caucasian appearance, about 175cm tall, of slim build, with long blonde hair and blue eyes.

She was last seen wearing a shirt and shorts.

Anyone with information about Lily’s whereabouts, or who walked the Bonnum Pic Walking Trail from Wednesday onwards, is urged to contact Moss Vale Police Station or Crime Stoppers.