Thanks to whom for what? The darkness? Not friends and family who are only so much flotsam. That would seem hypocritical. What kind of atheist would fall for that?
Isn't it obvious?
For since the creation of the world His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse.
If an atheist wants to just thank family and friends on Thanksgiving I say God Bless him and pray for the day that they see the evidence around us.