I really hope you find your cat, I remember how devastated I was when one of mine was missing for nearly 3 weeks, Christmas Day too[:0]
I was so upset, it was like I had lost a family member, I could not stop crying, I searched everywhere, in the snow, rain, etc We put up posters (with a reward) on all the lamposts, in shop windows, put an ad in the paper, even got the local radio to play an announcement, (maybe you could try this?) We rung RSPCA, even rung the council to see if any cats had been found dead at the side of the road[:(] I just wanted to know what had happened to him. In the end, the perseverance paid off, a lady rang up (she had seen one of our posters right outside her house!) and she had seen a cat sneaking under the decking in her back garden, and it was him, we got him back, although he was very ill, he is fine now, the cheeky monkey! So don't give up hope.