How many websites are there on the web world, which are offering social networking?

Hello, there are many social networking sites for people around the world the popular sites are

1 facebook

2 myspace

3 google+

4 twitter

5 youtube

beyond these 5 sites there are many sites which are also social networking sites used in various countries for various purposes these not only help to be socially active but also provides required information and helps in the research, are entertainment providing. some of them are open for everyone while some can be joined only upon invitation

academia.edu-site for researchers {open}

advagato- site for software developers{open}

travbuddy.com-for the travellers(open)

weeworld- for teens {open}

we read- books(open)

playfire- video games {open}

itsmy- mobile community blogging {open}

epernicus- for researchers {open}

cellufun- mobile game,applications {open}

audimated.com- music lovers {open}

dailystrength- for medical purposes {open}

these are the few popular websites in the world. they not only serve to connect among people but these sites also provides required information in a specific field