This age old question in itself is wrong.
Wrong because there is no universal definition for God. For hindus, it is one (or million) thing(s), for Christian it is another thing and so on. Even within a religion we have our own definition of God.
Mahakavi Devkota’s God was different from Kavi Shiromani Poudyal’s God. For some it could just be that feeling of inner peace; for other it could be a material existence that created us all and is the ultimate super power.
Buddha went in a quest to find the answer to his question and he must have narrowed it down to actually finding God; as that could be the ultimate quest. After over a decade of not finding God he realized that the answer lied within himself. Peace was his answer and he achieved this answer through inner peace within himself. He went to preach this knowledge, possibly without knowing that people will eventually take him as the incarnation of God later…contrasting the very theory that he concluded himself.

Coming back to the question, religion is a belief. Some people believe it others don’t. It is best to respect the beliefs of others and not force your own belief onto them. You can argue about the existence, or lack there of, forever and you will never reach a conclusion. I can easily offer an answer to somebody who claims there has to be a God and I can do so for the atheist as well. I will continue to respect the beliefs that my folks have and continue with my own.