Anika Haigh and more than 50 of Mr Tweddle's friends and family are helping with the search by talking to residents, door-knocking and plastering his picture around the streets of Leura.

"It is an extremely hard time however we are just keeping hope alive in our hearts that he will come home to us very soon," Ms Haigh told Fairfax Media on Tuesday.

"Hope is absolutely our anchor right now. That is everything we are holding onto and we are putting all our energy into help bringing him home."

Mr Tweddle, 23, from Cremorne, disappeared in the early hours of last Tuesday after leaving the Fairmont Resort in Leura.

The 23-year-old computer salesman, had gone out to dinner at Silk's Brasserie as part of a work conference and returned to the resort to continue drinking with colleagues in one of the rooms.

But the last time anyone heard from him was when he called a work colleague's phone about midnight and said he was lost in bushland near a main road.

Police said the phone call went for 17 minutes and was heard on loud speaker by four people who were trying to figure out where he was.

He has not been heard from since and his mobile phone is now either switched off or out of battery.

Hours later police launched one of the largest scale searches conducted in the Blue Mountains with the help of more than 800 volunteers in the past eight days.

"We are overwhelmed by the efforts from the volunteers and police," Ms Haigh said.

"We have had over 800 volunteers and bottom of our hearts we cannot thank them enough. We will be forever grateful."

Ms Haigh said she was confident Mr Tweddle would be found alive because of his determination and fitness level.

The pair braved three early morning boot camp sessions three times a week at North Sydney and Mr Tweddle was one of the fittest members.

"He used to make me get out of bed early - that fitness and his determination is the thing that will keep him going and bring him home to us."

Evidence of Mr Tweddle's popularity could be seen at the police command post which was set up in the Fairmont car park for a majority of the search.

Hundreds of friends, family and volunteers linger in hope around the site.

His father David and step-mother Michelle had flown from the UK to help with the search as had his mum Carol and her partner Clive travelled from Queensland.

"He is one of the most kind, caring, loving, and passionate person that I know and he is extremely determined," Ms Haigh said.

"He is a very loved person and we are touched and overwhelmed by all the friends an family that have come and helped in this situation."

Mr Tweddle's family and friends have taken to Facebook to appeal for any information. A Facebook page titled “Have you seen Gary Tweddle?” has almost 2000 likes.

Police have established another command post in Sinclair Crescent, Wentworth Falls which can be seen from the Great Western Highway.

Operation Crossway has already “twice covered” parts of the Jamison Valley closest to the resort with rescue workers searching dense bushland at the bottom of cliffs off Sublime Point Road, Nardin Street and Orchard Lane.

Police divers searched dams on nearby Leura golf course and the Rural Fire Service and State Emergency Service, and the Bushwalkers Wilderness Rescue Squad have helped to scour more than 14 square kilometres of bushland.

Blue Mountains Detective Inspector Mick Bostock said more than 80 volunteers and emergency service workers were still involved with the search on Tuesday.

He said police still held hope Mr Tweddle could be found alive and said the search efforts would be reassessed at the end of the week.

“We believe it's misadventure ... he's been injured and can't get help,” Inspector Bostock said.

“The best scenario is he's taken shelter and is waiting to be found.”

with Brenda Cunningham-Lewis