My favourite social network for getting traffic is current flavour of the month Twitter. I'd advise anyone starting a blog to create an account for their writing.
When you sign up, use the find people option to search for keywords like Film or Movie. "Follow" these people, but not too many in a 24 hr period or you'll get blocked.
Next, post some links to your writing. Twitter works by posting text messages with a maximum character count of 140. You'll be able to give a small clue as to your contact, followed by your link.
Your Twitter will grow slowly but as an example, I run one for a DVD company at the moment and, after a month, we have 560 followers. If I post a link, that link will get between 50-70 hits in a hour. The bigger the list of followers, the bigger the traffic. This site works as long as you temper your link posts with a few personal posts as well, to avoid looking too spam-like.