all good ideas.

I know how you feel, I was attached to Cookie after just 3 days!
(when she got sick after the 3 days here you would have thought I'd had her for years)

I feel so bad for you, I know how you must be so worried! and poor little lost kitty! have you called the humane society and other shelters in your area? put up posters, ask neighbors?
and yes, keep looking and calling. the poor thing, I wish I could come help you look for little Gus. your are(and Gus too) in my thoughts and prayers, for kitty to get home safely!