Many people question the very existance of God because they don't see Him. But we never question the existance of gravity or the wind. We don't see these things but we see what they do. The wind moves the trees, and gravity keeps us from floating away into space. So in that way what do we see God doing?
Well we must begin with the fact that we live in a finite universe. This means that our universe had a beginning and will have an ending. The law of thermodynamics states that all things in our universe are slowing down and decaying or dying. This is strong evidence that space, time, and matter in our universe had a beginning. If the universe was eternal, then things would not be dying. We also see that the universe is expanding out from a central location. This indicates a starting point. Every starting point or beginning requires a cause.
Skeptics will say "Big deal, that just supports the Big Bang theory." No it does not. The Big Bang theory basically says there was some cosmic cell of energy that exploded, and thus all the planets, stars and laws of the universe formed by accident. The first question I have is where did this cosmic cell of energy come from. The second question I have is that this theory violates the universal law of entropy. This law basically says that all things move from order to chaos. However the Big Bang theory reverses that law.
What does this have to do with God? Space, time, and matter are complex things that are held together by laws and ordered systems. We do not observe complex things like these forming by accident. We only see order created out of chaos by an outside intelligence who had a purpose for creating such an order. For example a computer could never have formed without a personal creative designer who had a purpose for it. Yet skeptics attribute much more complex systems such as life, space, time, and matter to a natural accident.
When we look in the mirror and see our eyes, and think about our inner systems such as our immune, digestive, nervous, and reproductive systems, we have to know these things were creatively designed. To attribute the complexity needed for life to exist to a series of accidents and coincedences is in my opinion the greatest folly of mankind. God is that intelligent designer. He has given us all kinds of clues to His existance. Creation is just one evidence. Some may still wonder why we can't see God. God is spirit and sin has blinded us from being able to see Him in spirit. Faith is the only path that will cure our blindness. No I have not seen God physically but I have seen Him working intimately in my life through answered prayers, His word speaking to me in amazing ways and just through amazingly coincedental events in my day to day life. I see now that these events are not coincedences but Godincedences.
You want evidence of God, just look at the complexity of nature and how everything works together. The laws of the universe require us to know there is a God. We are created by God with a purpose. That purpose is revealed to us in the Bible.