Acts 17:23 (AMP) - "For as I passed along and carefully observed your objects of worship, I came also upon an altar with this inscription, To the unknown god. Now what you are already worshiping as unknown, this I set forth to you."
God is real. In fact, all false gods are thought off because God does exist. Man would not have the mind or thoughts to create a god after themselves, if the real thing did not exist. You cannot have a copy or a counterfeit if there is not original.
Man today (and throughout time) have claimed that there is no God. They seek to refuse to accept His reality, yet even rejecting Him they are held accountable by Him. They may not acknowledge Him, but He acknowledges them. They may not believe in Him, but He believes in them. They may refuse the salvation through Jesus Christ, but He has redeemed all men. Jesus Christ on the Cross redeemed all men for God the Father, but unless a person personally accepts Him, they do not have the saving grace to spend eternity with HIm.
That is why Paul spent his life sharing the gospel with all he could. They did not know God (Athens), but Paul was going to try his best to make sure they knew about Him. Consider today, the people you come in contact with, do they know God? They may know about Him, may even use His Name (inappropriately), but do they have the saving knowledge about Jesus Christ? Is He their Lord and Savior? If not, how can you make Him known to them?