Silas’s name day is July 30, the feast of Silas the Apostle.
Churches that follow the Old (Julian) Calendar keep the same feast on August 12 of the civil calendar. See everything commemorated on July 30.
The saint behind the name

Silas the Apostle
July 30, Apostle, Σίλας
St. Silas, numbered among the Seventy Apostles, was a leading man of the Church in Jerusalem who was chosen to accompany St. Paul on his missionary journeys. He shared the Apostle's labors and sufferings, and at Philippi was imprisoned with him, praying and singing hymns at midnight when the earthquake opened the prison doors.
Name days: Silas
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.