Nobody has seen God and there were many atheists who doubt His existence. In spite of so much disbelief there are a majority of believers in the world. So God is proving to be stronger than the doubters.
None whatsoever. If there is a God, he's never shown himself and has never done anything that provides solid evidence that he exists. Science has also done a good job of explaining how the universe formed without him.
In fairness, various people claimed to have seen him, or heard from him. These claims, however, have never been independently verified, and are mutually contradictory.
Today the modern intelligent human is asking for proof which he/she can see. Since we cannot travel backwards in time, we cannot know for certain what happened in the past except to rely on the information received from our ancestors which could be distorted over time.