Such is the sustained nature of Foursquare's growth, the fact its userbase has now surpassed 4.5 million isn't regarded as groundbreaking these days.

Indeed, the revelation that its network has grown at an average rate of 375,000 new users a month since it launched a year ago was delivered as a side note to another announcement: Foursquare is expanding.

New dawn

"In the past year, we had a major growth spurt: from about 100,000 to over 4.5 million users; from a single phone platform to six; from 50 person Foursquare flashmobs to 1,000 person epic swarms; and we now have thousands of developers building on the the Foursquare API," the firm detailed in a blog post.

"The biggest challenge: hiring fast enough to support that surge. Despite growing from five employees to 35, we can't expand as quickly as we want."

As a result, Foursquare has opened up a new office in San Francisco, hiring a full team of engineers to staff its expansion.

Sign up city

More interesting than all of this, however, is that much of this growth has occurred in the wake of Facebook Places.

Since the social network entered the location field at the end August, Foursquare's userbase has grown by around 1.5 million users – a sign up rate of over 500,000 a new users a month.

That represents an acceleration of the monthly sing up rate Foursquare enjoyed in 2010 pre-Facebook Places, with the app having previously averaged 455,000 new members a month between April and August.

[source: Foursquare]