Daimler's Car2go car sharing service launched in San Diego back in November, 2011 and changed from an all-electric fleet to gas cars this past March. Despite the shift, drivers didn't show up. As Car2go put it, "unfortunately we have not seen enough adoption of our unique one–way carsharing service here to continue operations at this point."
Car2go's services in other cities (like Seattle and Columbus) remain in operation, and anyone with an account in San Diego will (as before) be able to use vehicles in those cities. There are 42,000 Car2go members who were using 255 vehicles in San Diego, but the company needed more to make it work. Car2go said that, "We truly hope that as more people around the world like you adopt carsharing and embrace all its economic and environmental benefits, we might one day resume our service here."
You can read the announcement email below.