If you are feeling hungry and the hunger is increasing then you can say, "I am starving". But if you have too much hunger then you can say about your condition (may be you are not able to say that due to weakness), "I am starved" :)

If you are very hungry, it's usual to say that you are 'starving'. You'd say 'starved' in the sense of 'The poor dog starved to death'.

In colloquial U.S. English I've heard both. I can't even say which is more common. They both mean "I'm hungry and I want to eat right now."