On Wednesday evening, Facebook announced what appeared to be a stake in the heart of competitors Foursquare, Gowalla and other checkin based social networks. However, according to Foursquare CEO, this just might not be the case after all.

On Thursday, the first full day after the Facebook Places announcement was made, Foursquare saw the most new signups ever for a single day. This is of course according to a tweet made by Foursquare CEO Dennis Crowley, but there is no reason not to believe it.

The most likely reason so many people decided to sign up to Foursquare, is because they had never heard of it prior to the Facebook Places announcement. Foursquare just got the best marketing pitch they have ever had. When a company like Facebook copies an idea that you have, it must mean you are doing something right. Facebook, which has over 1/2 billion users, announced to the world that they have created a checkin service like that of smaller company Foursquare.

Many people hadn’t even heard about Foursquare, but loved the idea that Facebook Places had, so they decided to compare the two services. It should be interesting to see what membership numbers do for the rest of the month. Foursquare just might survive.