Kimberly,
It sounds like you've done just about everything.  Only one other suggestion
I could think of.  Children are out and about more than adults.  It is very
possible that one child has found Bongo (we've had ferrets found several
miles from where they were lost).  Try tacking up notices around schools,
playgrounds, wherever young children congragate.  The offer of a reward will
sometimes bring armys of children into the search, especially if the offer
seems big enough to child.
 
Don't blame yourself (I know that's hard.)  We've had one of ours escape on
three different occasions (different one each time).  We've been fortunate to
have each one stay in our yard.
 
A suggestion to any others that loose their ferret, would be to put their
cage, bedding, food and water outside as soon as you know they've gotten out.
 Leave the cage door open. The ferret may stumble across it's own scent while
initially roaming about and find it's way back to the cage where it will stay
(at least for a while).  They find their cage a place of security and will go
to it if they can find it.
 
We wish you all the luck in the world in finding Bongo.
 
Dick and Joan Bossart
[Posted in FML issue 0984]