Hello Laura and
to Purrs - sorry that you have found us under these circumstances.
Take a look at Sam's excellent tips here:
http://www.purrsinourhearts.co.uk/index.php/topic,305.0.htmlI think that is is still early days for you as Amber has only been missing since yesterday. If this is out of character check places where a cat could possibly get stuck i.e. your neighbours sheds and garages etc.
My cat Cleo disappeared for a couple of days but I was not too worried as this was not unusual for her, I heard miaowing in my daughter's bedroom and she had actually been locked in a cupboard, so even in your own house they can nip into a wardrobe when you are not looking and accidentally get shut in.
A friend of ours found a cat in the back of his van and he took the cat to a local rescue, they are known for getting into cars, vans etc.
Good luck with your search and I hope that Amber comes home soon.