In order to stop subject movement you need a fast shutter speed. You can't use anything slower than 1/250s if you're panning with a blurred background. If you want something completely frozen then try 1/1000.

If your lens doesn't allow you to get these shutter speeds because the maximum aperture is too small then you can increase the ISO. This will bring you more noise in the picture but with the latest generation of DSLR's this isn't a problem up to 1600ISO at least.

Lets take an example of a not very bright day:

1/125s f5.6 at 400 ISO (basic setting)
1/500s f5.6 at 1600 ISO (increase ISO with 18-105 or 70-300)
1/500s f2.8 at 400 ISO (with 70-200 f2.8)
= same picture