Re: Slight pain and weak erection since using a Penis Extender around 8 months back:
There are many kinds of damage that penis extending stretching can cause besides just to nerves. And you hadn't even got to stretching to injure yourself, you were just applying the device?
Before talking about any peripheral nerve growth stimulants that might help nerve function, how sure are you that it's not vascular damage or some other sort of damage? Some things that might help heal nerve damage are entirely different from those that help heal vascular damage. Gentle exercise and good eating are good for any sort of injury. Vitamin B12 is probably good for both nerve, vascular, or connective tissue damage (not that those are the only sorts of penile injury possible).
If it were me, I would want a doctor (better a urologist) to examine things to make sure it appears good and whatever treatment I try is safe for my condition.