Paul, Silvanus, and Timothy, to the assembly of the Thessalonians in God the Father and the Lord Jesus Christ: Grace to you and peace from God our Father and the Lord Jesus Christ.
and Silvanus: "A ’chief man among the brethren’ (Acts 15:22), and a ’prophet’ (v. 32), and one of the deputies who carried the decree of the Jerusalem council to Antioch. His age and position cause him to be placed before Timothy, then a youth (Acts 16:1; 1 Timothy 4:12)" (Jamieson, Fausset, and Brown 384). Silvanus is always called Silas in the book of Acts.