The penis is not a muscle; you cannot build it up through exercise, however it certainly can be stretched.
One method of stretching is to hang weights from your penis for a specific period of time per day. Sound painful, guess what, it is. I also found that the time required to leave the weights hanging from my penis was incredibly difficult given the sheer logistics of it. It is definitely not a multi-tasking type of deal if you know what I mean. Can you imagine if your privacy was disturbed or if you had to do some housework, you better not bump into anything!
Lastly think of the process ina logical manner. As you stretch something it gets thinner. What about the width and girth that women crave as well? Do you really want some long skinny pencil looking penis? I certainly didn’t.
CONCLUSION: Even if this method is successful, the gains will only be in length and will be at a sacrifice to your width and the overall look of your penis. You want a girl to do a double take when she looks st your penis due to it’s size NOT becasue it looks freakish and odd, I don’t recommend it.