I've been struggling so much in my relationship with God that I've questioned his very existence. I've been praying and praying, no answered prayers. I've been asking God to speak to me, nothing ....

I've asked God to reveal himself to me.. Nothing

I need help , where is God. Does he even exist at all?

God may need you to work on you first before he answer your prayers, the fact that you even question his existence shows you lack of faith in him. He knows what's best for us even though we can't see it, it may be that what you are asking for is not best for you. Give it all to God and let him work it out for you at his timing, that's having faith in him, not questioning his existence or you wanting him to jump at your command right now, it's the other way around.
Lord have your perfect will be done in this person's life and in their prayer request. Let them know for sure that you are a real God who hears us and answers us, but when you think we are ready for your answer. May they get more into your word where they can understand stand what you expect from us, and give them the wisdom they need, and your peace. I pray in Jesus name, amen.

Jesus I come in agreement with this prayer request in your precious name amen.