Flights to/from Volos (Nea Anchialos) airport are officially announced on the airport’s website.
In most cases, the flights scheduled are once a week from Paris, Brussels, Tel Aviv, Amsterdam, Geneva, Munich, London, and Vienna and are mostly charter flights.
The airport’s website has the full listing in easy to digest form here: http://www.thessalyairport.gr/en/flights-en-menu.html
Some of the flights are scheduled for the entire summer and have already begun service. Others are very short term; for example the Geneva flights appear to be only in July and August.
See for yourself.