But Sullivan said that the number of people that they've added may be 25 to 50 percent fewer than what they've added in recent months.
Based on earlier figures from Facebook, he said that the site usually reports that it gains 20 to 25 million active users each month. But since announcing the recent changes, he said Facebook is on track to only add 13 to 15 million active users per month.
He said that Facebook told him the 10 million figure was "rough" and that it may be too early to tell whether the privacy issues are having an impact on active users.
Still, Sullivan told ABCNews.com, "The numbers didn't add to a positive spin from what I see. It added up to a negative spin."
The latest backlash traces back to Facebook's developer conference a few weeks ago, when CEO Mark Zuckerberg unveiled several changes intended to make the Web more social and personalized by expanding Facebook's presence to other sites.
On thousands of sites, including ABCNews.com, a "social plug-in" now lets users "like" content and see what their Facebook friends have liked, directly from those sites.
On three sites piloting an "instant personalization" feature, a user's profile information and friend list are automatically read by the site and used to shape the user's experience.
But over the past few weeks, some of those data-sharing changes have drawn increasing attention from critics, who say Facebook needs to give its more than 400 million members more control over the personal information they disclose on the site.
"With great power comes great responsibility and sites like Facebook have great responsibility," Sen. Charles Schumer, D-N.Y., said at a news conference a week after Facebook's announcements. "In my view, it ought to be the user who determines who gets what information, not Facebook."
Joined by three other Democratic senators, Schumer sent a letter to Facebook, urging it to revisit the new policy and make it easier for users to control and protect their privacy.
One of their top concerns was Facebook's "opt-in" policy, which means that personal information is automatically shared with some partner Web sites unless the user goes through the process of disabling this feature.
In addition to sending a letter to Facebook, Schumer asked the Federal Trade Commission to create guidelines for Facebook and other social networks to follow.
In a letter responding to the senator, Facebook said it takes privacy very seriously and that its new products give users "unprecedented control over what information they share, when they share it and with whom."
But privacy advocates have pointed out that this is not the first time Facebook changes have triggered their concerns. In 2007, when Facebook unveiled Beacon, which tracked user behavior on other sites and shared the information on Facebook, user dissatisfaction was so strong that Facebook ultimately backpedaled and Zuckerberg apologized.
In 2009, the social network announced another set of privacy changes, which again sparked complaints from privacy advocates and Facebook users.
Charlotte Crockett, a 29-year-old Facebook user from the Netherlands, is one of more than 94,000 people to join a group called "Facebook, Respect My Privacy!" which was created by a MoveOn.org organizer and urges Facebook to reconsider its policy changes.