Not on Facebook?

Online pioneer Len Kleinrock, shown with a processor that was used to develop the Internet, said Facebook is fine for the grandkids, but it’s not for him.

NEW YORK — Don’t try to friend MaLi Arwood on Facebook. You won’t find her there.

You won’t find Thomas Chin, either. Or Kariann Goldschmitt. Or Jake Edelstein.

More than 900 million people worldwide check their Facebook accounts at least once a month, but millions more are Facebook holdouts.

They say they don’t want Facebook. They insist they don’t need Facebook. They say they’re living life just fine without the long-forgotten acquaintances that the world’s largest social network sometimes resurrects.

They are the resisters. “I’m absolutely in touch with everyone in my life that I want to be in touch with,” Arwood said. “I don’t need to share triviality with someone that I might have known for six months 12 years ago.”

Even without people like Arwood, Facebook is one of the biggest business success stories in history. The site had 1 million users by the end of 2004, the year Mark Zuckerberg started it in his Harvard dorm room. Two years later, it had 12 million. Facebook had 500 million by summer 2010 and 901 million as of March 31, according to the company. That staggering rise in popularity is one reason why Facebook Inc.’s initial public offering todayis one of the most hotly anticipated in years.

Facebook still has plenty of room to grow, particularly in developing countries. About 80 percent of its users are outside the U.S. and Canada.

But if Facebook is to live up to its pre-IPO hype and reward investors who are clamoring for its stock, it needs to convince some of the resisters to join. Two out of every five American adults have not joined Facebook, a recent Associated Press-CNBC poll said. Among those who are not on Facebook, a third cited a lack of interest or need.

If all those people continue to shun Facebook, the network could become akin to a postal system that only delivers to houses on one side of the street. The system isn’t as useful, and people aren’t apt to spend as much time with it. That means fewer opportunities for Facebook to sell ads.

Len Kleinrock, 77, said Facebook is fine for his grandchildren, but it’s not for him. “I do not want more distractions,” he said. “As it is, I am deluged with email. My friends and colleagues have ready access to me and I don’t really want another service that I would feel obliged to check into on a frequent basis.”

Kleinrock said his resistance is generational, but discomfort with technology isn’t a factor. After all, Kleinrock is arguably the world’s first Internet user. The University of California, Los Angeles professor was part of the team that invented the Internet. His lab was where researchers gathered in 1969 to send test data between two bulky computers — the beginnings of the Arpanet network, which morphed into the Internet we know today.

“I’m having a ‘been-there, done-that’ feeling,” Kleinrock said. “There’s not a need on my part for reaching out and finding new social groups to interact with. I have trouble keeping up with those I’m involved with now.”