Don't fret too much, yet. Ferrets are domesticated creatures and when they get out they often don't stray too far. Get outside with your pals and keep looking. Mine have returned to their open nest box before now, when they've got tired and hungry.
Good luck
Although I can agree with Bert I've lost fezzers this way twice, both times my fault the buggers obviously found a better life Sorry for your loss mate but these things do happen