A.T. Robertson Commentary 1 Thessalonians 5:12

"But we beseech you, brethren, to know them that labor among you, and are over you in the Lord, and admonish you;" — 1 Thessalonians 5:12 (ASV)

Them that labour among you (τους κοπιωντας εν υμιν). Old word for toil even if weary.

And are over you in the Lord (κα προισταμενους υμων εν Κυριω). Same article with this participle. Literally, those who stand in front of you, your leaders in the Lord, the presbyters or bishops and deacons. Get acquainted with them and follow them.

And admonish you (κα νουθετουντας υμας). Old verb from νουθετης and this from νους (mind) and τιθημ, to put. Putting sense into the heads of people. A thankless, but a necessary, task. The same article connects all three participles, different functions of the same leaders in the church.