Arnold,
There are some untouched issues here.....
As soon as you can, identify the damaged area. This is called damage control. The effort is not so much to correct the issue but to prevent it from extending to other areas.
I very much doubt that the tank is any kind of fiberglass as none of the resins used in those processes are acceptable for potable water use.
It is highly unlikely that the whole tank froze to the point of failure.
It is very possible that the tank plumbing froze enough to crack and drain the tank. If this is the case, you may be able to repair just that section of plumbing.
Best of luck.
Matt