How do I use social network for marketing?

Hi, my question might be really basic, but I'll give it a try anyway.

How do you actually use social networking for marketing into practice? For example, I have a stumbleupon account. After I wrote a post, I'd go to my account, enter the details, and save it. But if I want to post to 20 networking sites, and I write 2 posts a day, I will have to do that 40x.

And who will read it? For twitter, my posts are tweeted automatically, but I have no follwers.

Or is there a way to automate the process? Can I submit to whichever social networking site I want automatically when my post is published?

Thanks.

There is AddThis service you can use to share your post or page among many social networks and bookmarking services quickly.

But anyway you need readers and followers

Okay... I have that, but usually I submit each article to the SB sites myself to my own accounts. For Reddit and Stumbleupon I am able to generate some additional traffic, but I don't know whether I might be blocked for spamming at some time for doing this.

You can create groups in Facebook, fan pages in order to drive quality traffic to your site. You can also post quality tweets in order to derive quality traffic from Twitter.