This is timely question as I'm sure some of those in Haiti are wondering the same thing. First, I'd encourage you to do is pray for your friend. You have to rely on God because there is nothing we can do or say - in our own wisdom - to make your friend believe in Jesus. Pray that God would open his spiritual eyes because your friend may believe nothing is happening, but this does not mean God has ceased to work.
We are human beings with finite senses and intellectual capacities. So when we pray, we often think that God only answers our prayers IF He answers them our way or when we can visibly see the results. This is simply untrue. I believe God listens to our prayers; and answers them according to His time and in His way. So I'd respond to your friend by telling him to be patient and wait upon the Lord.
The second thing is to point your friend to Jesus. Jesus came to our world to suffer with us and for us. When people suffer, there are two usual responses:
(1) “You’re suffering because God is judging you. You’re doing something bad, and God is angry with you.”
(2) “You’re suffering and that means there is no God. Or at least, He doesn’t care about us.”
When we look to Jesus, however, we see neither of these gods. We don’t see a condemning God; we see a God of love that bears the punishment for our sin. We don’t see a missing God. We see a God who is willing to enter a world of suffering to suffer with us and for us. No other faith or philosophical system makes such a claim. So whatever your friend is going through, let him know that Jesus has been there too. Jesus knows what it's like to betrayed; to lose a loved one; to be hated; to be beaten and to die horribly. And that's why when your friend prays to Jesus, he can rest assured that God is listening! He is not idle nor incapable. He is a compassionate God who listens to and answers prayers in his sovereign, perfect timing.
I'd also recommend you listen to this sermon & read this article - so you're equipped to handle your friend's questions about suffering in general.
Friend, God has given you the great gift of ministering to your friend in his/her time of need. Pray hard. Study hard. And listen attentively. Sometimes the way a person gets to know Jesus isn't through what you say, but what you don't.
[Answered by Pastor HM]