I have been in your situation more than once--don't beat yourself up,
some of these little guys are real escape artists!
 
I found these suggestions really helpful when looking my missing ferret:
Concentrate your search close to home.  Put up lots of posters with a
picture (I discovered many of the neighbours don't know what a ferret
looks like and may mistake them for wild animals).  Speak to as many of
your neighbours in person as you can--perhaps one has seen your ferret or
spoken to someone else who has.  Above all, don't give up hope--ferrets
can be very resourceful about finding shelter, even in this weather.
 
Good luck!
Debby
[Posted in FML issue 4803]