An agnostic is different. First of all, there are several different categories of them. An agnostic in general is not sure if there is a God or not. Some believe that there might be a God but have never really seen any evidence, so they can not be sure.
I think many of the un-churched people in our lives would fall into this category. They don't deny God, but they can't be sure that there is a God either. They are undecided. How do we reach these people for Christ? How do we reach atheist for Christ?
Ultimately it is the working of the Holy Spirit in their lives, but God can work through us as believers to show them Jesus. What it really comes down to is Christians showing the love of Christ through our relationships with these people. It might even be simple acts of kindness.
These are just some thoughts. Any comments?