Holman's Christian Standard Bible says at I Thess 3:2 that Timothy is "God's coworker [Greek: synergon] in the gospel of Christ."
First, you are citing a textual variant. Many manuscripts substitute "servant" as opposed to co-worker. While I do think that "coworker" is the better reading, there is no small mess in the manuscripts in relation to this particular verse.
Second, given the entire corpus of Pauline literature, it is laughable (almost to the point of shooting milk out of one's nose) to think that Paul means what you're taking him to mean. Gordon Fee explains:
But what Paul almost certainly intended is what one finds in the TNIV, that Timothy, who ultimately belongs to God, is being commended first of all as Paul’s and Silas’s own “brother,” and further as their co-worker “in the gospel of Christ.” At the same time he is God’s person in all this missionary activity. Although Paul’s phrase for this activity may mean, as the TNIV has it, “in spreading the gospel of Christ” (which as an English idiom means to evangelize), he far more likely intended, “in the continuing work of the gospel of Christ,” which would thus include his past and present visit to Thessalonica.
Gordon D. Fee, The First and Second Letters to the Thessalonians, The New International Commentary on the New Testament (Grand Rapids, MI: Wm. B. Eerdmans Publishing Co., 2009), 116.
In no way can Paul be meaning that Timothy is in some way participating in the life, death, and resurrection of Christ to affect the salvation of the Thessalonians.
The Archangel