Google may be built on an algorithm for taming the Web, but yesterday the company added social features that will let your friends help determine what ranks high in the search results you see. The approach requires Google to know the social connections of its users—something that so far is not a core feature of the company’s products or uppermost in the minds of people using them.

Google’s new social tool is the +1 button, which it wants you to click to signal which search results and Web pages you appreciate. The button will appear alongside every page listed in search results, and later on sites across the Web (enable +1 on your account now here). Your +1 clicks will be used to boost the ranking of that page in the results friends see. To Google, “friends” means people you are connected to by the company’s e-mail or instant-messaging service or its Twitter clone Buzz. The new +1 service will eventually appear on other Google products like Maps and YouTube, says Google.

In design and intention, the +1 button is a close imitation of Facebook’s Like button, which appears both on Facebook’s site and on pages across the Web as a way for users to share content with friends with a single click. Facebook says that every week more 250 million people engage with Facebook’s tool for external sites—most often via the Like button.

Google’s plans to shape search with +1 have a precedent, too. Microsoft’s Bing search engine has since late 2010 used Like-button data in a partnership with Facebook, in which Microsoft owns a stake. The results of some types of searches—for example, for restaurants—promote or highlight pages that have been Liked by a person’s friends. To use this feature, the person must be logged in to Facebook.

“I think +1 is a big step forward,” says Vivek Wadwha, a visiting scholar at the University of California, Berkeley, School of Information, who last month organized an event examining the problem of search spam. However, it is unclear whether Google has enough information about its users’ social connections for the strategy to be very powerful, says Wadwha. “It is clear that Google is on the defensive and is trying its best to give consumers what they need,” he says. “But it is at a disadvantage because it doesn’t have a social graph in the same way Facebook does.” Microsoft’s close relationship with Facebook gives it access to more powerful and comprehensive data, says Wadwha.

Not only does Facebook have more users enrolled in its Web-wide scheme, but its users have more incentive to click Like buttons than Google users do to click +1. Clicking Like shares a link to that page with Facebook friends, or even adds something—say, a movie—to your Facebook profile. Clicking +1 only adds a link to your Google profile page, a widely ignored feature that Google wants to encourage more of its users to embrace. It is possible to view what Google considers your “social circle” at a dedicated page, but there is no way to edit that list of friends without deleting e-mail, chat, or Buzz contacts.

At the same time that Google tries to expand the role of its profile pages in people’s lives, its new social features will come under attack from spammers seeking to manipulate +1 data, says Rich Skrenta, cofounder of search startup Blekko. Manipulating search results to extract revenue from pages stuffed with advertising—much of it channeled through Google’s own advertising system—is big business today. Software bots and low-paid human labor are used to create extra links to those pages, co-opting the main criterion by which Google ranks pages.

The value of a social approach comes from having a network of real people acting genuinely, says Skrenta, something that Google needs to find a way to ensure. “Facebook has done a very good job of this to date, since they actively police identity and people carefully monitor their Facebook contacts and drop contact with people who spam them,” he explains. That’s a stark contrast to the state of Google’s social links, which are largely invisible to users, many of whom maintain multiple accounts.

However, if +1 works, it will be a valuable signal, he says. “If they can boot up the system and keep the spam out, it could be another interesting source of social ranking data, along the lines of Facebook Likes, Foursquare check-ins, tweets, and so forth.” At least part of those stores of social data is made publicly available for other technologies to use, says Skrenta, whose own search engine uses Facebook Likes much the way Bing does. “I would be interested to know if Google intends to open this data up as Facebook and some of the other social players have,” he says. So far Google has not signaled that any +1 data will be similarly made available.