Which social media site dominates social media and is used so extensively that most organizations must have at least some presence on it?

Face-book

Explanation:

*Face - book which was started by Mark Zuckerberg, with his fellow Harvard College students has a reach of only * Harvard University when it was started. Today it is one of the largest social media site but its exact membership is ambiguous because of the fake user accounts. Most of the organizations used it promote their products to the large number of members of Face_book.