But right in the Book of Acts we have a quote from that letter which the Jerusalem church sent out, don't we? Acts 15
Also > Colossians 4:16 > Paul mentions letters which were to be shared.
So, from this I can see how there could have been other sharing, though it is not recorded in detail.
Well, ones in Romans knew of Paul and even had developed in faith before meeting him, Paul himself says in Romans 1:8-12. So, ones had faith, but they did know of him.
And Paul says the Thessalonians themselves were "examples" (1 Thessalonians 1:7) to people they reached. So, yes ones Paul reached were reaching others. So, from this I can see that ones reaching could have told people about Paul.
So, I am curious who you mean, by saying Christians did not know of Paul, since he got the ministry to Gentiles started.