My heart goes out to you...
You have obviously spoken to all neighbours, etc. And probably repeatedly too! But I once had a female cat that liked wandering off - she always knew where she was and she always came home, but... I got calls from folks three miles away from my house who'd been feeding her and thought she was lost.
Just saying that on your door to door enquiries, don't stop at the end of the block. Or town, come to that.
Welcome to Purrs. And good luck.