Albert Barnes on 1 Thessalonians 1:2

We give thanks to God always for you all. Rom 1:9.

Making mention of you in our prayers. Eph 1:16. It may be observed here,

(1.) that the apostle was in the habit of constant prayer.

(2.) That he was accustomed to extemporary prayer, and not to written prayer. It is not credible that "forms" of prayer had been framed for the churches at Thessalonica and Ephesus, and the other churches for which Paul says he prayed, nor would it have been possible to have adapted such forms to the varying circumstances attending the organization of new churches.