Experience with Small Rotator Cuff Fraying/Tear in Pitchers

I can only offer my personal experience if it is of any help...

I had a tear in the acromioclavicular joint and of the supraspinatus tendon a couple of years ago.  It was a acute tear, rather than a wear issue like you are describing.

My ortho gave me the option of trying rehab before doing a surgical repair, and that was the route I chose.  I saw a therapist a couple of times a week for about two months, and did a ton of exercises on my own as well.

Most of the work in the beginning was to restore range of motion, and then it progressed to strengthening the muscles in the rotator cuff.  Many of the exercises were from the "Thrower's Ten", or variations of them.  You would be surprised just how little weight you can move in some of those exercises, because they really isolate muscles that rarely get any attention in traditional workouts.

After a few months I was back to having a functional arm without too much pain. A couple of years down the road and I'm able to throw pain free and workout without any restrictions.

The only thing I have noticed is that I don't have the ability to get any distance on long toss any more. I might get 150 feet or so if I really heave it.  Prior to the tear I would throw with my oldest out to about 225 feet without much effort. Now he throws at 300 and I just catch it and put it in the bucket. No pain, just can't get the distance.  Of course the fact that I am getting older probably is a factor in there as well.

I can throw bp all day though without any issues, so I guess I don't have reason to really complain.

I would say that a 16 year old would have way more success than I did.  The important thing is to get with a therapist who is experienced with throwing athletes, and follow the rehab and strengthening program religiously.  Even if it means taking some time off from playing, you definitely need to deal with the issue before it gets any worse. 

Highly recommend you read up on anything written by Eric Cressey or Mike Reinold in regards to shoulder instability (laxity) and proper rehab/prehab for rotator cuff injuries. If your son takes great care of his arm and stays with prehab shoulder work, he will be just fine. It really is not that much extra work but takes a commitment. The problem is that most athletes revert to their old ways once an injury heals. Tell him to stick with shoulder work recommended by those in the know as long as he continues to play baseball and he will definitely minimize the risks of further injury.