14 How then will they call on Him in whom they have not believed? How will they believe in Him whom they have not heard? And how will they hear without a preacher? - Romans 10:11-14
The equation is this. We call on Him whom we believe, we believe on Him whom we've heard of, we heard of Him by way of a preacher. So what about those who are never preached to? I would argue that everyone has been preached too.
19 because that which is known about God is evident within them; for God made it evident to them. 20 For since the creation of the world His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse. 21 For even though they knew God, they did not honor Him as God or give thanks, but they became futile in their speculations, and their foolish heart was darkened. - Romans 1:19-21
Creation itself preaches to men, sent by God (v19) to the point that His power and divine nature have clearly been made known by these preachers (v20, cf Psa. 19:1-2) so they are without excuse. These men actually reached a point of knowing God (v21) but it's what they chose to do with that knowledge which is pivotal. And of these men it says they chose not to honor God. But rather they "suppress the truth in unrighteousness" (v18), "exchanged the glory of the incorruptible God for an image in the form of corruptible man...birds...creatures" (v23) "they exchanged the truth of God for a lie" (25) "they did not see fit to acknowledge God any longer..." (v28).
It's not that men are unaware, but rather they make a deliberate choice. In the case of these men above they chose to "suppress", "exchange", and to disregard the message preached to them. However some are recorded as heeding the message of God before the gospel of Jesus Christ was fully revealed. Here's some to name a couple.
Abraham was preached too before the gospel of Jesus Christ was made fully manifest and what does it say about him? "Then he believed in the Lord; and He reckoned it to him as righteousness." (Gen. 15:6).
Job heard the message preached by nature and it says of him "There was a man in the land of Uz whose name was Job; and that man was blameless, upright, fearing God and turning away from evil." - Job 1:1
And one more (though there are others) from the new testament.
14 A woman named Lydia, from the city of Thyatira, a seller of purple fabrics, a worshiper of God, was listening; and the Lord opened her heart to respond to the things spoken by Paul. - Acts 16:14
Lydia was a worshiper of God before ever being spoken to by Paul.
Maybe some of you were raised in a Christian home or a home professing God from your birth but for those of you that weren't, did you remember being aware of God before anyone brought you the gospel? I do. I remember being very young (guesstimating 8-9 yo) sitting in my front yard examining the muscles in my legs and arms and how they bent my elbows and knees and I was thinking to myself that this (my body) was an impressive invention.