Annie, welcome to 3FC!
You might like to check out the Exercise forum. If I'm not mixing forums up in my overloaded brain, I believe there is a monthly walk/run challenge thread, so you'd look for "March Walk/Run Challenge" thread, and I think you would be able to connect with others that are setting a similar mileage goal. The challenge threads, which can be found all over the boards, are a great way to make closer connections to other 3FC users and really get that support network going. Of course, we're all here for each other, but it makes a difference when you feel like you know a person a little better.
You might also find some kindred spirits on the Weight Watchers forum, in Diet Central. Of course, you can browse the forums, and should jump in any place that feels right to you!
Best of luck to you, Annie, with your goals for weight loss and exercise!