I seemed to have strained a shoulder muscle while throwing yesterday. Is there anyway to loosen these muscles up so I can throw again?

I can’t say I’m anything of an expert and probably wouldn’t listen to myself, but I would think stretching and rest would be in order.

How did you do it? Did you not warm up enough? I’ve done that before where I was eager to get throwing and trying things and I was throwing too hard after only a couple warm up throws. Anything I’ve had has been elbow though, not shoulder.

You see what happens when you try to warm up too quickly??? I’d say give the arm a rest, don’t do any throwing for a week or so, just stretch it out—s-l-o-w-l-y. Then get back into throwing, but go easy at first, then you can step it up.
What I used to do when warming up before starting a game—or even before I would have to come into the game in relief—I would start with a few minutes of an easy game of catch. Then, a little at a time, I would start putting more and more stuff on my pitches until, when I got to my last five or so, I would be throwing at full power (such as it was; I was a snake-jazzer). By then I would be ready to go out there and pitch.
The whole point is, easy does it.