A significant search at Enfield State Park started on Thursday morning in a bid to find her body, Victoria Police said.
The 51-year-old was last seen leaving her home on Eureka Street to go for a run in Canadian State Forest on the morning of February 4.
Samantha Murphy has not been seen since leaving her home for a run on February 4. (James Ross/AAP PHOTOS)
Officers will focus on "an area highlighted by intelligence derived from a number of sources", with crews investigating a site 10km south of the previous unsuccessful search at Buninyong Bushland Reserve in March.
The public has been asked not to join the search, which is about 20km south from the Murphy family home.
Crews scouring the area include those who specialise in missing persons, search and rescue, the public order response team and the mounted branch.
Cadaver dogs have been called in to help.
About 50 searchers are combing the state park for signs of Ms Murphy's body with one dog dashing around and inspecting small pits in the ground believed to be mine shafts.
The off-the-track area is covered by dense forest with foliage casting shade over the ground filled with damp leaves, smaller trees and fallen tree trunks.
The search area includes dense bush and a number of old pits and mineshafts. (Joel Carrett/AAP PHOTOS)
It can be difficult terrain, with the area that once housed tents and diggers now dotted with abandoned mine shafts from the gold rush era reclaimed by wildlife.
The Murphy family was told of the new search, which follows unsuccessful efforts in the Canadian State Forest.
About midday some officers began returning to the Napoleons Recreation Reserve about 10km from the Enfield site for a lunch break after hours of searching.
The operation is expected to go on past 4pm.Police in March charged 22-year-old tradesman Patrick Orren Stephenson with the murder of Ms Murphy at Mount Clear on the day she went missing. He will return to court in August.
Stephenson is the son of Orren Stephenson, who played 15 AFL games for Geelong and Richmond between 2012 and 2014.
Detective Acting Superintendent Mark Hatt described Thursday's effort as an extensive large scale search that built on targeted operations in other areas.
Cadaver dogs are being used in the operation to try and find the body of Samantha Murphy.(Joel Carrett/AAP PHOTOS)
"I want to assure those in the Ballarat community that police remain focused on doing everything we can to return Samantha to her family," he said.
The regional western Victorian city has been rocked by a series of tragedies this year including Ms Murphy's disappearance, a mine collapse that claimed the life of worker Kurt Hourigan, the death of mother-of-five Rebecca Young and bushfires in surrounding areas.
On April 5, 23-year-old Hannah McGuire was found dead in a burnt out car at Scarsdale.
Ballarat locals will stage a rally in the centre of the city on Friday evening as an act of solidarity in the fight to end violence against women.
A description of the event on social media said women do not feel safe in Ballarat.
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