This is probably a retarded question but I'm on a map with no hills or whatsoever and I can't find any coal, at all. I've been mining for about an hour I think under my house in the dark. Whenever I exit to get new resources for pics or something like that my mine is full of zombies... Any help?
You should try strip-mining. Or try to mine straight down. When digging straight down, you don't have to place torches, because you have daylight right above you. And if that all doesn't work, you can try to make a new world. I recently made a new world, with "pot-weed" as seed (I haven't discovered this seed, someone else on this forum did). There's a huge mountain, with a lot of coal veins. And there are sugar canes/reeds, and cacti! This is probably te best seed, so delete your old world, and start a new world with this seed!
A good way to get ores, is digging a 1x1 hole, all the way down to bedrock. You'll still get sunlight in, since there isnt anything to block it away, and since there are so many coal veins in the world, and they are so big, you will come across it 90% of the times you do it (just a rough estimate, since i always get coal from it, but there are of course places without coal.