A mystery man who wrote a letter to police may hold the key to finding missing Jordan Moray, detectives say.
The missive was signed with the name "Kevin Humphreys" and contained information officers believe could be helpful.
Attempts to identify the author have proved unsuccessful, so police are appealing for him to get in touch.
Keen hiker Mr Moray was last seen on 29 July in Bro Deg, Cwmbach, near Aberdare.
Det Insp Dai Cole of South Wales Police said: "Hopefully, Mr Humphreys, or somebody who knows him, will see this appeal and make contact.
"In his letter, he provided information which could be significant without him realising it.
"Jordan's disappearance is a mystery and any new leads which may help us understand where he is at this time will be helpful."
Mr Moray, 32, was reported missing on 2 August by his family, having last been seen by them on 24 July.
The alarm was raised after concerned relatives visited his unlocked flat.
A gaming machine had been left on. His phone was also in the Cwmbach property.
His family said this was out of character.
Searches for Mr Moray have been complicated by his enjoying spending time outdoors.
Potential search parameters have proved expansive and challenging.
Det Insp Cole said: "We know Jordan enjoys walking in places such as Cwmbach, the wider Aberdare area, and as far afield as Brecon.
"It is not unusual for Jordan to walk in excess of 20 miles a day, usually off the beaten track on mountain trails.
"With this in mind, I would like to direct my appeal to those who also enjoy the outdoors, who may share his enjoyment of the same things and places."
In the weeks before his disappearance Jordan was seen getting into a blue/purple Ford Fiesta which was driven by a woman who had visited his home.
He was later dropped off by the woman, who was in her 20s with long dark hair.