Grant Redpath, who runs Tranent Pet Supplies in Haddington Road, kept his pet reptile in the shop.
While the animal lover was out the back of the building grooming dogs on Thursday, his snake, called Snake, was snatched from his tank.
“I just want my little fella back with me so I know he is okay,” he said.
“He’s not poisonous at all and very friendly.”
“I have a section in my shop for the reptile products which is where he was,” he continued.
“I have another snake in the shop, she is a California king, but they never got to her.
“I remember that day seeing three hooded guys walking away from the shop, but didn’t think anything of it.
“But then when I went to check on Snake he was gone.
“The glass was closed , the vents were sealed, he couldn’t have gotten out, it’s impossible.
“Someone took him.”
He said if someone sees his pet for sale and buys him, he will pay the cost of Snake plus the £100 reward to have him back.
He is a corn snake and has yellow and white skin.
Commenters have since taken to social media to shame the thieves.
One person said: “This is so sad that people can steal from these guys, as they work very hard.
“Its despicable that people think it’s ok to help themselves to people’s pets.”
Others have described the theft as "cruel" and "tragic."