Not really. For one, the Sophists were not especially an ‘organised body’. There wasn’t a “Sophists Association” or anything of the sort. Secondly, Sophists were known primarily for their teaching of the ability to persuade through public speaking. Atheism wasn’t a core component of their philosophy, indeed philosophy wasn’t a core component of their teaching. Sophists were generally known for teaching people how to argue for anything at all. This is why Plato, and to a lesser degree Aristotle, objected so much to Sophists – in Plato’s view they had little regard for truth and the practice of philosophy.