That's why I said challenge or group support. In group support, you are accountable to the rest of the members of your group. You can currently make your FitDay profile visible to friends, but you can only go look at them one at a time.
In a group setup, ideally you could see everyone's progress stats on one page, and how they're meeting whatever goals they've set for themselves, and how the group is succeeding overall. Perhaps a running forum for encouragement, etc.
A challenge between friends can make it a little more fun if that's your personality. A prize at the end, even if it's just a token item or monetary amount, is still rewarding to many people.