Why do you want to know so badly? What value do you believe you will gain from this knowledge?
(And why do you insist on "virtually" shouting the words WORLD WIDE WEB? In online communications, all-caps are generally interpreted as shouting.)
The vast majority of social bookmarking sites are basically useless, both in terms of adding "link juice" to your own pages or in sending you direct traffic. Knowing they exist will do you no good, unless you're just looking for the satisfaction of being aware of a whole ton of obscure websites.
If you did, in fact, search through Google, you must not have done a very thorough job. When I search for a list of social media sites, the very first listing is for Wikipedia, which has a fairly comprehensive list
. That should be more than enough to get you started with whatever project you might be contemplating.
Beyond that, I'm not sure if anybody has a complete list. In the first place, such a list would be a lot of trouble to compile and maintain given that sites come and go all the time. Second, there's no actual benefit to be gained from going through all that effort. Third, had someone decided to go through the trouble, believing there to be some benefit, they would be unlikely to share the fruits of their labor with the world at large, for free. (Either because they want to retain for themselves the benefits, however fictional those benefits might be in real life; or because they know there are people out there who are crazy enough to believe in these fictional benefits and who will spend money to gain this useless information.)