Tosker escaped from my supposedly cat proof enclosure during his first night with me, because he was so afraid, and it was pointless looking for him as there was no way he would have allowed himself to be caught
but the second night I saw him at the far end of the garden, so I put food down there for him
and he came back for food every night, and I found out after a couple of weeks that he had taken up residence in my neighbour's garage
Gizzy might well be quite close still too, as nervous cats want to hide rather than wander off - so I would suggest you set up a feeding station outside where you can spot him from a distance if he comes to it
if he does then at least his immediate needs will be met, and you can move on to the next stage
my Tosker took 3 months to get into the house, and a year later is the most cuddly loving cat I have ever had