Why do we believe in God, if there's no proof that anyone has ever seen him/her?

God invisible to human eyes. Well, would you expect to survive a journey to the sun? No, you would burn up long before you got there. God created the sun. Hence, he is far too powerful to be viewed by human eyes. That is why God says in his Word: “No man may see me and yet live.”​—Ex. 33:20.

Also, you can't see air but you can't breathe without it.

I know why we Christians believe.  I have no clue what you believe.

Of course no-one has ever seen Him. He is pure Spirit, with no physical body. We can't see spirits, just as we can't see gravity. But we can experience the effects of gravity, and the effects of God in our lives.

The premise of the question is in error.  People walked with Jesus, He is God, so people have seen God.  And He is not a female.

Him/Her? Seeing how your avatar name is Bill, I assume you are a guy. Were you and your Dad a He/She? God the FATHER had Jesus Christ, a SON.

Sadly, even if someone produced a photograph of God, taken by the Hubble Telescope perhaps, that would be rubbished as proof. Atheists would claim it had been Photo-shopped, or concocted, or interpreted wrongly. Consider the thousands of photos that had to be computer-manipulated to produce one photo showing a black hole in outer space. From many locations on mountains on earth, series of photos were taken, all focused on one particular spot in space where, it was suspected, lurked an invisible black hole. There had to be perfect weather over a series of nights for all the photos, which were all fed into a computer to be put together to produce one that, it was said last year, showed an invisible black hole. Do we doubt such evidence? No! Well, a few might. But we acknowledge that there is reasonable evidence to now conclude that such a thing as an invisible black hole exists. But - to this day - nobody has actually SEEN a black hole.  That's the point.

Same with the invisible God, who is Spirit. He is too glorious, too 'other' for mortal eyes to behold and remain alive. He created us with eyes that can see certain things, but lots of invisible things cannot be seen by us without artificial aids. Spiritually blind people cannot either see God or even understand how He is to be contacted. Yet God has enabled sincere seekers to 'see' Him with spiritual eyes of understanding. He has dealings with such ones. They have access to Him via the wireless prayer system He created thousands of years before the Internet. They read His words in the written communication He caused to come together over 1,600 years, written by some 40 men (most of whom could not concur.)

And, supremely, He sent the Word of God, His unique Son, to become a man on Earth, to show us God through Himself and what He did and said. But spiritually blind people have no understanding because they are spiritually dead. In their human thinking, they don't even know where to look, or how to look. Yet all they have to do is get down on their knees and humbly pray for God to help them, repenting of their pride and sin. Asking in the name of the now resurrected Jesus Christ is vital.

If you take the number 0 (zero) it means there is no number. But then why is it the most used one (1)? 

God may not show us proof of his existence. But he is all around us.

Have you ever seen your great great great grand father? No? Then, how do you know he existed? I'm not Christian, but you have proof he didn't exist.

Who is this 'we' you speak of, Mr. Bill? But really it's not strictly about seeing or not. There is no significant, establishing evidence of a god, and that's the problem.

Is the only way to know something is to 'see' it?  Can our eyes be deceived?

I've never seen a place called "France" with my eyes -- but I believe that it exists.

I've never seen "love" with my eyes -- but I've felt its effect or its absense

I've never seen a magnetic field with my eyes -- I've seen measurements of it, but never the field itself.

I've never seen a gravity wave, but I'm limited by it.

I've never seen the Wind, but I've seen it blow around leaves or dust into my eyes.

I've never seen 'justice' - but I know when I haven't received it.

It MAY turn out that the MOST important things in life - we never actually see.

But we can feel or experience their affect and KNOW that they exist through experience, reason, deduction, history, and other types of 'knowledge'

You are RIGHT - God can't be directly seen -- But maybe that's is because he is BIGGER than that.

Maybe we are called to 'know' him in OTHER ways besides mere experimentation or visual confirmation.

____________________

You say that there is NO PROOF.

But how much in life do we really have proof of?

Most of the time we have arguments in favor of, and arguments against. We weigh the arguments and come to our own decision.

Often times people want 'proof' because it overpowers reason - it makes things EASY for them. If we have 'proof' then we don't need to think any further - the decision is all but made FOR US. 

TYPICALLY...

Reasonable and open people talk about arguments. Closed minded people tend to deal with 'proofs'

When someone doesn't WANT to believe in something - what is typically the 1st words out of their mouth?

"Prove it!"

RIGHT?

How do people who want to discover the truth talk about ideas?  As proofs? OR as 'arguments' and 'evidence' and 'conclusions'???