You can find Thomas in HKO in West Stars Plain, north-west of Paris. You will have to walk quite a bit to meet him. He has stuff for you to do and might even offer you a special house, if you are willing to make some boots for him. But it depends on something like chance it seems - not everyone will get a house from him...
Thomas is good friends with Hello Kitty. He is known as a rather hasty little bear, but he also often makes everyone laugh with his jokes.