I do not understand what you mean when you say, "they tend to stretched out to the penis."

I mean that when I shave the shaft base , a few days later, i see new ones growing up and i think that from time to time shaving the shaft will be full of hair.

So, does anyone knows something about that?

it's relatively safe to shave the penis. But you can expect the hair to grow to grow back. I know of some people that have had laser treatments to completely irradicate the hair. This may be a option for you. As you have found out that there are hair folicles on the shaft of the penis. By shaving you may have stimulated the dormant folicles.