Often, I've found, the hardest person to talk to about spiritual matters is the one who feels absolutely no need of God. Unfortunately, more and more people are going in this direction as our society becomes more and more secular.
But this doesn't mean a person with no apparent interest in God is living a full and satisfying life. In fact, the opposite is often the case. They get caught up in a mad scramble for happiness, or success, or approval, or pleasure, or any of a number of other things that consume them. Their goal is like that of the rich man in one of Jesus' parables: "Take life easy; eat, drink and be merry" (Luke 12:19).
The tragedy, however, is that eventually they will discover these things can't give them lasting happiness. If they are honest, they'll be forced to say with the writer of Ecclesiastes, "I denied myself nothing my eyes desired ... (yet) everything was meaningless, a chasing after the wind" (Ecclesiastes 2:10-11).
Pray for those you work with and ask God to give them a hunger for Himself. Pray, too, that you will be a witness to Christ by the way you live -- by your Christlike love, peace, joy, patience and so forth. Then don't be afraid to question their goals, pointing them instead to Jesus, who came "that they may have life, and have it to the full" (John 10:10).