Google is a latecomer to social networking but its new site, Google+, is growing much more rapidly than Facebook, Myspace and Twitter did in their early days, technology experts said Tuesday.

While Google+ may be the fastest-growing social network ever, it remains to be seen, however, whether it can pose a serious threat to the social networking titan Facebook, which has more than 750 million members.

Andrew Lipsman, vice president for industry analysis at tracking firm comScore, said Google+, which was launched by the Internet search and advertising giant on June 28, had 25 million unique visitors as of July 24.

During a panel discussion on Google+ hosted by Wedbush Securities, Lipsman said it took other social networks much longer to reach 25 million users: 22 months for Myspace, 33 months for Twitter and 37 months for Facebook.

"Obviously, this is a very strong growth trajectory," Lipsman said.

He cautioned, however, that Google "has a really large user base it can build off of" with its one billion users worldwide.

And it still has a "really long way to go to be competitive with Facebook," Lipsman said.

"Google+ is the fastest by a long shot but it's important to realize that fastest may not always be best," he said. "Sometimes, that slow build can lead to a strong network effect that pays long-term dividends."

Most Google+ users -- 6.4 million -- are in the United States, followed by India with 3.6 million, Canada with 1.1 million, Britain with 1.1 million and Germany with over 920,000, according to comScore.

Lipsman said many Google+ users appear to also be users of Google's email program Gmail and display a "very strong early adopter profile."

He said the ratio of men to women is about two to one and that 60 percent of Google+ users are between the ages of 18 and 34.

In the United States, the highest numbers of Google+ users are in the tech-savvy cities of San Francisco and Austin, Texas, he said.

Steve Rubel, executive vice president for global strategy and insights at public relations firm Edelman, said Facebook is not "vulnerable immediately" to Google.

"I don't see (Google+) taking significant share from Facebook in the next 18 months," Rubel said.

At the same time, "what we have seen is that over the years there's never been a social network or community that has had significant staying power," he said. "There's always a shuffling every two or three years, a changing of the guard.

"We saw it with Myspace," he said of the one-time social networking leader that has been eclipsed by Facebook and hemorrhaging users ever since.

Rubel said Google was compelled to try its hand at social networking because Facebook is restricting the access of its search engine to Facebook content.

"What's happening is more content is being created behind Facebook's walls than ever before and a lot of that content is invisible to Google," he said.

"Conceptually, at least, they're building kind of an alternate Web... There's also an entire Web that is app-based on mobile phones. That is also invisible to them."

Rubel said it was conceivable that more content would be invisible to them in five or 10 years than what the search engine can see today when created on Facebook or inside apps.

"So they had to make a play to get more people to create content on their site," he continued. "It's to get more people to spend time on Google."

In unveiling Google+, Google stressed the ability it gives users to separate online friends and family into different "Circles," or networks, and to share information only with members of a particular circle.

One of the criticisms of Facebook is that updates are shared with all of one's friends unless a user has gone through a relatively complicated process to create separate Facebook Groups.