Missing hiker Niels Becker spent months getting fit and strong enough to go for "the longest walk" he'd made so far in Victoria's high country for his birthday.
The last time his parents heard from him, he sent them a text from a hut near Mt Stirling, and now he's been missing for nine days.
His parents Johanna and Peer Becker urged anyone who might have seen their son to help the search.
"Niels had been preparing this hike for months and was very much looking forward to spend his 39th birthday in the high country," Peer Becker told reporters in Melbourne on Thursday.
"If anybody remembers seeing a solo walker, please contact us."
Niels left the house he shares with his parents on October 24 - one day before his birthday - intending to walk the Macalister Springs area.
The experienced hiker was due back at his vehicle on October 29 but failed to show and was reported missing.
"He mentioned that reception was terrible in his last SMS, and was meant to send another text the day after, but that hasn't happened," Mr Becker told reporters.
The Beckers said they remained hopeful about their son's situation, but that was fading.
"I have worried about him before, but after Tuesday we are not as optimistic", Ms Becker said.
Described as an independent person, Niels' love of the high country had moved him to plan his longest walk yet.
Neils was described as "focused on his writing and music composition" before the hike, and his parents said he was emotionally "on top of the world" before leaving.
Police said he was believed to be well equipped for the walk and familiar with the area.
"He's hiked many times around that area. Sometimes alone, sometimes with his sister," Mr Becker said.
The search resumed about 7am on Wednesday with a team of more than 70 including police, the State Emergency Service, Bush Search and Rescue and the parks department.