I used to be agnostic. My parents(my father is catholic and my mum is protestant) raised me without religion. During my teen years, I was an atheist. I believed that since I cannot see God, He must not exist. And the wars fought over the years over religion also led me to believe that God would not allow such a thing to happen, but since they did happen, there must be no God. As I got older, I started to think about how the Earth was born. Everything in the universe, including the universe itself, has a beginning, and a subsequent end. I began to wonder, how did the universe begin? It certainly didn't create itself. I also thought about how life began. We certainly didn't create ourselves, and never has anyone seen something come from nothing. This universe was obviously created, and it was obviously created by Someone who has a whole hell of a lot more power than any one of us. And finally, I started thinking....what if hell really exists? And what if I would have to go there for all eternity? Just because I didn't have definitive proof of it's existence didn't mean that it wasn't a possibility. This question sometimes made it hard for me to sleep. But basically at the time, I was smoking a lot of weed and didn't really delve further into the subject more than that, and it was later that I would learn about Islam, and while you could say I found Islam, but the truth is, Islam found me. Insha Allah I will post my story on how I became a Muslim in another thread.
