So what are some of the top social media sites today that business owners can tap into?

In a recent study, eMarketer, a market research firm, ranked the popularity of social networking sites in the US and came up with the top 20.

Interestingly, as of Mary 2009, Facebook has replaced MySpace as the most popular site among internet users. Facebook’s unique visitors doubled to over 70 million in the 12 months ending May 2009.

Also, while Twitter showed the most dramatic growth over this time period, its visitor level is still less than a third of Facebook and MySpace.

For businesses looking to utilize social media marketing, it may be useful to take a deeper look at the top 3 sites and their visitor demographics.

1. Facebook

Online since March of 1997, Facebook is the 4th most trafficked site on the internet, with users spending an average of 26 minutes a day on the site (based on Alexa statistics).

The site appears to attract a younger more affluent demographic, with a heavy representationof users aged between 18-24.

2. MySpace

Ranked 11th by traffic, MySpace users spend an average of 19.5 minutes daily on the site, which was started in 1996. Much like Facebook, it tends to attract young adults (relative less affluent however than Facebook users).

3. Twitter

Unlike the top 2 sites above, Twitter users spend only 8.5 minutes each day on the site which has a traffic rank of 25.  The site tends to attract a slightly older audience, those between the ages of 25-34 with males being more over represented than females.

This quick analysis shows that knowing the user demographics of these sites is critical in helping business owners determine if this is the right target audience for their products or services.

Since social media marketing requires a significant time commitment, rather than following the herd and targeting the top ‘most popular’ sites, it pays to spend time researching each social networking site’s audience before jumping in.

Tools such as Alexa, Compete or Quantcast provides useful  statistics and site demographics which businesses can use to conduct market and competitve research.