What is gossip?
Gossip is the spreading of rumors and lies about others.
It is also rumor or talk of a personal, sensational, or intimate nature.
So far in the television series of Gossip Girl, the 'Gossip Girl' has not been revealed. There was a major attempt by Serena to unmask her, but 'Gossip Girl' outplayed her and announced that Gossip Girl was everybody, because everyone had sent in tips and contributed to the making of 'Gossip Girl'. The voice of 'Gossip Girl' is Kristen Bell though.
No, Gossip Girl is not a real site. Gossip Girl and it's characters are a work of fiction, written about in the Gossip Girl series by Cecily von Ziegesar. Consequently because of the book and television series popularity, many fans have made their own Gossip Girl sites. But I'm sure that there are internet sites similar to Gossip Girl, which track 'it-girls and boys' and spread gossip and rumors, whether they be true or false.