some basic properties of a string

I know different vibrational modes of a string correspond to different
kinds of particle and different energies of a string correspond to
different masses. A string vibrating vigorously would result in a
heavier mass of a particle than a string vibrating less vigorously. So
how is the size of a string related to the size of a particle? Clearly
a string is smaller than any particle. Second, is a string truly
vibrating? Particles can be at rest.