Theagenes’s name day is January 2, the feast of Theagenes of Parium.
Churches that follow the Old (Julian) Calendar keep the same feast on January 15 of the civil calendar. See everything commemorated on January 2.
The saint behind the name
Theagenes of Parium
January 2, Hierarch, Θεαγένης
St. Theagenes was Bishop of Parium on the Hellespont. In the persecution under Licinius he was pressed to serve in the army and to deny Christ; refusing, he was imprisoned, tortured, and finally drowned in the sea.
Also celebrating on January 2
These names share the feast, many of them other forms of the same name:
What to say on a name day
The Greek wish is Χρόνια Πολλά (Chronia Polla), “many years.” A call or a short message on the day is what people remember. See name day wishes you can send and what a name day is.