For not only has the word of the Lord sounded forth from you in Macedonia and Achaia, but your faith in God has gone forth everywhere, so that we need not say anything.
– 1 Thessalonians 1:8 (ESV)
Paul is thankful for the Thessalonians. In the verse above he is explaining the fact that they have become imitators of Paul and the others so that they have become examples to the other believers.
The effect is astounding. The word has gone out from them in turn. Also their faith has gone out. I am taking this to mean that there are new believers all over the surrounding region as a result of their witness. This is a missionary-minded church because of the gospel they received.