There is a group called the Prayer Guardians.
Check out this thread:
Prayer Guardian Thread
There's nothing special about this group, other than we encourage each other. You have to "cruise" the Prayer Forums yourself. Most members try to fast the 1st and 15th of each month.
The Administrators have asked that we (the Prayer Guardians) not just reply "I'm praying for you" to every post we pray for. If you have something substantive to say, go ahead, but they want to keep the post counts down. So for lots of prayer requests, we are praying anonymously.