A.T. Robertson Commentary Philemon 1:24

"[and so do] Mark, Aristarchus, Demas, Luke, my fellow-workers." — Philemon 1:24 (ASV)

The other "co-workers" (συνεργο) here (Mark, Aristarchus, Demas, Luke) are all named in detail in Col 4:10-14 with kindly words.