It's called spam. You didn't consent, and you can do assorted searches and report it to the hosting ISP. If you're in Europe, you can also report it to the appropriate government department. You did not consent to them contacting you, you did not hand over your details, just because a friend did does not give them the right to harass you via phone, mail or email.
It's not just "lesser" networking sites. I have more than one email address, and Facebook spammed me for *months* before I finally twigged how to tell them to go away. They'd culled the addresses from a close friend's address book as he hadn't realised the implications of "have access to my email address book".