Social bookmarking type sites are booming right now, and seem to be fluctuating in traffic as well. Each network has a different demographic no matter how much the same they all seem. Not all social networks are created equal and to have a strong social media marketing plan you need to know what type of demographic each has, and what type of content will generally perform better. All statistics gathered from Quantcast.

1. Digg
Digg is pretty much the most popular social bookmarking site. Statistics from Quantcast estimate that Digg receives about 21 million unique visitors a month. The digg audience is mostly males (63%) between the ages 23-34, with a household income between $30,000 – $100,000. I’m sure the audience has changed drastically from the time they came online. Digg like all other sites has certain content that appears more on the front-page, these include lists (top 50.. etc.), politics, Apple articles, and interesting photos.

2. Propeller
Propeller (once Netscape) is second to Digg ranking in with 1.4 million monthly unique visitors. Like Digg, Propeller also has a predominantly male audience with 54% of traffic most of whom are age 45-54. The older audience of Propeller also have deeper pockets with 55% of them making over $60,000. The front page also seems to pertain more to the older crowd with most of the news being politics, business, economy, etc.

3. StumbleUpon
A Quantcast top 5,000 website StumbleUpon brings in 1.2 million unique visitors a month from the U.S. The audience is male biased (51%) and has a relatively equal spectrum in age. 30% of traffic comes from ages 18-34, 33% from ages 35-49, and 33% from ages 50 and up. Also interesting about this age range is it’s effect on the average income. 30% of StumbleUpon users have an income of $100,000 or more. 47% of which, have no college education (no joke.)

4. Fark
Just missing out on the top three is Fark.com. Fark has grown considerably and seems to be retaining their traffic well. With over one million monthly unique visitors, its bigger than sites like Del.icio.us, Reddit, and Newsvine. They attract a middle aged audience, mostly Caucasian, and are less affluent (53% $30K-100K). Fark also has a much higher male population (72%) than most of the other sites. They have a more interesting brand of popular content focusing around “interesting, bizarre and amusing news stories, along with regular photo manipulation contests”.

5. Newsvine
Not quite reaching a million users yet, Newsvine comes in at number four. A top 10,000 site that reaches over 946K U.S. unique visitors monthly. They have a middle aged, Caucasian audience that is less affluent. The site attracts a skewed male audience (55%) and 46% of them have an income of $30,000 – $60,000. Also interesting is that Newsvine has a very large business readership. 31% of their readers are business with over 4.5K large businesses alone.

6. Reddit.com
Another top 500,000 site is Reddit. With 856.7K unique visitors a month, Reddit attracts a 57% male audience that is between the ages of 35 and 49 (35%). Within Reddit’s audience 65% have a household income of $30,000 to $100,000. Similar to Digg, Reddit favors content related to political, business, and offbeat/celebrity news.

8. Clipmarks
Raking in 493.9K unique visitors monthly, Clipmarks comes in at number seven. The top 5,000 website appeals to a male biased audience (57%) with a pretty equal division of income through all ages. The largest of the groups (28%) taking in $30K – $60K.

7. Del.icio.us
Although the olders Del.icio.us is not the most popular, ranking in with 37K unique visitors a month from the U.S. The audience is again mostly male (53%) and the largest age group is those between 35 and 49 (33%.) Use of Del.icio.us seems to be dieing off pretty quick lately and Quantcast shows that 92% of their traffic is passers-by meaning people are there for a few seconds and leaving.

9. Blinklist
Blinklist.com has seen a huge traffic plunge over the last few months and fell out of the top 10,000 sites. Down from over 560K in June of 08′, they now take in just over 131,000 unique visitors a month. A higher percentage of males (61%) make up the audience bringing in $60,000 to $100,000 on average. The site appeals to a more educated, more affluent, more male following.The typical visitor reads Salon, patronizes cduniverse.com, and visits killmyday.com

10. Shoutwire
Just making the list is Shoutwire with 20.4K unique monthly visitors. Shoutwire has a 58% male audience that is slightly younger with 63% of users between the ages 12 and 34. Even with the lower age range, the audience claims a 4 way split of almost 25% of the audience in each income bracket.

Obviously Digg is the champ here. They take in more traffic than the other nine combined meaning they should defiantly be a part of your social media marketing strategy. Digg also sees the largest amount of ad revenue and they continue to grow. This should give you a good base for what demographics apply to the top 10 sites, which should then give you a good idea how to generate content for them.