Where in the Bible does it say that one should have a good group of friends to keep him accountable? I had a friend who said I should stop seeking my friends' help for accountability and just ask God. If that is true, why does God talk about the church and community? I think you do need accountability among friends. I would like to tell him this, but I really wish I had Bible verses that said this.
"Two are better than one, Because they have a good reward for their labor. For if they fall, one will lift up his companion. But woe to him who is alone when he falls, For he has no one to help him up. Again, if two lie down together, they will keep warm; But how can one be warm alone? Though one may be overpowered by another, two can withstand him. And a threefold cord is not quickly broken" (Ecclesiastes 4:9-12).
"Accountable" is not quite the right word to describe the relationship between friends. Being accountable means that you are answerable to another person and that you are liable to that person if you don't meet expectations. "Accountable" means that one person is in a position of authority over the other. Each person is accountable to God, but we are not always accountable to each other.
What the Bible describes is that we watch out for each other. A friend doesn't let those he knows to wander off into sin. There are going to be times when true friends disagree, but that is because they care about each other. "Open rebuke is better than love carefully concealed. Faithful are the wounds of a friend, but the kisses of an enemy are deceitful" (Proverbs 27:5-6). There will be times that I must take a friend to task because he isn't doing right, but it doesn't mean he is answerable to me for the choices he makes -- for those decisions he is answerable to God.
Having friends makes you a better person. "As iron sharpens iron, so a man sharpens the countenance of his friend" (Proverbs 27:17). Friends challenge you to reach further than you thought you could go. Of course, you need to be careful who you claim as friends. You don't want people around you who push you toward sin. "He who walks with wise men will be wise, but the companion of fools will be destroyed" (Proverbs 13:20).
But you are right that the church exists to build its members up. "And He Himself gave some to be apostles, some prophets, some evangelists, and some pastors and teachers, for the equipping of the saints for the work of ministry, for the edifying of the body of Christ, till we all come to the unity of the faith and of the knowledge of the Son of God, to a perfect man, to the measure of the stature of the fullness of Christ" (Ephesians 4:11-13). The word "edify" means building up or improving. "Therefore let us pursue the things which make for peace and the things by which one may edify another" (Romans 14:19).