New Facebook Groups not anymore support "Message All Members" Service, we have no idea why is that, though the Old Groups Support still this Service .... so we found out how to " Send Messages to Members in your newly created groups" ....
1) First Open Facebook.com
2) go to your group where you are admin (the group that you created")
3) in the address copy the Last big Number in the end of the link (i.e if your group link is "http://www.facebook.com/home.php?sk=group_110735405669068 ,then the number would be 110735405669068) which is your group number.
4) in the same address bar paste this link (http://www.facebook.com/inbox/?compose&oid=your_group_number) ... OK ?
5) Have Fun