Amanda, 22, and her boyfriend moved into a top floor flat along Beach Road last Wednesday.
She found Missy missing the next day.
The former Bangor university student said: "We have looked everywhere in the flat and in neighbouring gardens. She may have curled up somewhere to try to keep warm but I am really worried about her survival chances.
"There are a lot of cats around here and she may be attacked by seagulls."
Amanda, who graduated from Bangor in 2004, is working as a health care assistant but has set her sights on a career in zoology.
She added: " Missy seemed happy enough the last time I saw her in her tank. I had changed her water and she sometimes curls by the bowl or up inside a log.
"Then on Thursday afternoon, just as I was going out, I realised she had gone.
"I checked the vivarium and found she may have been able to open a sliding door which wasn't closing properly because of a small piece of bark.
"Because we had only just moved in we left a skylight to the roof open.
"She may have got out that way but she could be hiding somewhere in the flat. We just don't know."
Anyone with information can contact Amanda on 0786 8717378.
