We are struggling to answer this very stubborn question. Why? Because we have realized after examinnig the literature recovered in the 1940s from Nag Hammadi, Egypt, that the rubric "Gnosticism" is a misnomer. It is a modern rubric that contemporary scholars have invented, rather than a word that describes a historical religion. Scholars built our modern understanding of Gnosticism to help us describe groups in the ancient world whom the leaders of the apostolic churches identified as deviant or heretical.
We understood these "heretical" Christians as participants within a larger religiosity, an umbrella religion we called Gnosticism. Gnosticism came to represent for us a form of religion in the ancient world that had turned against Judaism and Christianity, a perversion of traditional morality and piety as well as theology. It was described by scholars in the last century as a form of religiosity characterized by a negative view of the world and human existence, succumbing to nihilism and yearning for everything spiritual.
But this "golden bough" had broken. Analysis of the Nag Hammadi texts has shown us that there is no generic Gnostic religion. Rather there were a variety of Jews and Christians who were esoterically minded and yearned for the experience of "gnosis" - a direct meeting with God - and they had varying relationships with the apostolic churches or the synagogue. They all appear to have formed conventicles, study circles, or lodges in which they met for initiation into the mysteries of the Kingdom. But some of these people remained active members of the apostolic churches or synagogues, while also participating in the esoteric lodges. Others left the churches and synagogues, and only attended the lodges. These lodges were very distinct from each other in terms of social location, ritual performances, and even theological systems.
Even though there was no Gnosticism, I don't think this means that there were no Gnostics. So we must be very careful not erase the Gnostics in our post-modern reconsideration of Gnosticism as a mega-narrative that we created. What we need is to rethink the Gnostics and remap the second century so that it makes sense with the Nag Hammadi literature and the normative discourse that the Fathers of the apostolic churches were putting into place to suppress those whose Christian religiosity did not match their own. So yes, there were Gnostics. But who they were still remains to be fully understood.