The penis is not a muscle, it is an organ. No amount of wanking will result in a bigger penis, unless you found some way to mess with the gland related to retaining blood in that region....
2/3 of the penis is made of this muscle tissue called corpus convernosum
and the pubococcygeus muscles are reponsible for the ejaculation, Penis isn't a gland but it's an organ & there is many organs which are muscles as the heart
but I don't think that Steroids have a direct effects on the penis