Thank's vs Thanks

We often find this word our daily email communication. What's wrong with the words? Which one is the correct one according to "The should be English" grammar?

People use this word to express thanks a lot. The correct word to express thanks a lot is "THANKS". "Thank's" is not correct because thank is a singular noun. For plural noun is no need to use single apostrophe before ‘s’. So the correct one is THANKS not THANK’S. We can not say book’s but books for many books