Digital Trends – By the estimation of Ancestry.com co-founder Paul Allen, the Google+ network is looking at a total of 18 million users of the invitation-only social network by the end of Tuesday. Yesterday, the service added 763,000 new users which constituted the slowest day of growth since Google opened up the floodgates on July 6. The growth rate has dropped 50 percent from the peak of public interest, but Allen notes that Google hasnât attempted to actively market the service yet. Instead, Google is focused on product improvements and testing according to Allen.