Their seems to be two websites called Secret London, but I followed the one displayed on the Facebook page. This was a website called secret cities, which of course included a number of cities. London is the only city that is live on the website so far, and their are links to the rest of the secret cities Facebook pages. It seems the idea of Secret London and Secret Cities is in its prime (it was only founded two years ago). I think that Secret London is a fantastic concept, and a good way for Londoners to share their favourite places of the city. I think that it could do well with the appropriate branding and promotion.
Twitter is a great way to spread the word, as it allows people to communicate quickly and ask fellow followers for their advice.