Three-year-old Olly – who had only been with his Ilkeston owner a few days after he was adopted from a foster kennel in Doncaster – bolted from her garden when she opened its gate on August 13.
The Bosnian cross-breed was last seen on CCTV footage in the Walton area of Chesterfield on September 2.
Leverne Vasey – who is part of a group called Dog SOS Derbyshire – said: “Olly is still missing and we’re urging people to share this appeal and keep an eye out for him – he could be anywhere.
“His owner is very upset and just wants him home.
“Fingers crossed there will be a happy outcome.”
Helen Buckland, who is also part of the group, thinks Olly could be trying to make his way back to his Doncaster foster kennel.
She added: “We’re hopeful he will be found.
“The problem is we don’t know which way he’s heading as he can do up to ten miles a day.
“Hopefully he’ll settle somewhere soon then we can put a plan in place to catch him.”
Helen said it was common for foreign rescue dogs to run off – as they are often spooked by unfamiliar surroundings.
She is urging anyone who sees Olly not to approach him but to call her on 07934673790 or 07814734867 so she and other experts can bring him back to his worried owner.