Foursquare is reportedly looking to raise between $50m and $100m in a Series D funding round that would value the company at $700m-$800m, although investors are said to be sceptical.

TechCrunch reports that the company has been taking VC meetings as it looks to raise money for engineering resources and expansion. However, the site claims that VCs have been less than impressed with Foursquare’s recent growth rate, which has not improved after the service’s June redesign. Foursquare reported 15m registered users in December 2011, rising to 20m in April 2012 and 25m last month.

Foursquare did not confirm the rumours of a funding round, although it said in a statement, “Our numbers have continued to go up, especially since we made Foursquare Explore available to everyone on the web. People use Foursquare over a million times daily to find where to go, and over 5 million times daily to share where they are.”