I've been in a similar situation and made some big mistakes, so I'll speak out of my own experience.
1. Do you love your brother, is there any wrong motives -search your heart.
2. Are you the best person to rebuke or correct him, is there a leader in the church or a respected elder, relative or friend that would have better footing.
3. Have you prayed for him, has God confirmed this in your heart, as long as it's in your mind and not on your lips in prayer this is a definite red light.
4. Can you restore him gently? Sometimes its easy to shoot off the cannons and take cover and wait for the smoke to clear, but Galatians makes it clear that we should only correct someone if we can do it in a gentle way -of course sometime surgery is painful, but if your motives are pure, you love your brother, you are the best person to confront him and you are filled with the spirit then you'll be on the right track.
5. The last thought is this: do you have all of the information. In my situation I only had a piece of the picture, from my own perspective, it's easy to see sin and say 'that's sin' but it's entirely different to see our brother's situation and need... have you talked to his friends, his family, his peers... have you talked to him in a non confrontational and concerned manner? Instead of coming out gun's blazing it might be enough to say 'I'm concerned about you right now, would you like to talk?'
That's it for me... I almost had to leave the church I am in because of what I did when I rebuked someone I didn't meet any of these criteria, and the relationships are still not restored... be clear that you have the proper footing before proceeding.