NEW YORK — Facebook’s reach is wide but not deep. Few users surveyed in an Associated Press-CNBC poll said they click on the site’s ads or buy the virtual goods that make money for it.

More than 40 percent of American adults log in to the site at least once a week. In all, some 900 million people around the world are users, but many of them don’t have a very high opinion of Facebook or trust it to keep their information private.

Users’ distrust limits the value of the site’s ads. Advertisers want to target their messages to the people most likely to respond to them, and the more Facebook knows about us, the better it will be at tailoring those ads to our interests.

Yet in the poll of U.S. adults published Tuesday, three days before Faceook launches its hotly anticipated initial public offering, only 13 percent said they trust Facebook “completely” or “a lot” when it comes to keeping their personal information private.

A majority, 59 percent, said they trust Facebook “only a little,” or “not at all.”

Users’ desire for privacy and Facebook’s need to target advertising aren’t necessarily opposing interests. Facebook doesn’t expose information about its users directly to advertisers. Instead, it effectively accepts missions to deliver ads to groups of people. It’s up to Facebook to figure out how to find those people.