“It’s not that I’m a saint, but I try to go out of my way if it’s reasonable,” he said.

Some digital Samaritans have to work to get around barriers that are set up to protect people’s privacy. Shannon Kokoska, 39, dropped her wallet on a city bus in San Francisco in January and, later that night, before she knew it was gone, received an e-mail message from the man who had found it. Two of her credit card companies had declined to give him her address or phone number, so her white knight had sent her a message on Facebook.

“It’s nice to be reminded of that story,” said Ms. Kokoska, who was recently robbed of her iPod on the same bus.

Many airports and transit systems are using similar strategies. Miami International Airport takes queries for lost items over the Internet, and also uses the Web as its primary tool for locating passengers who have lost items.

Ernesto Alonso, the terminal operations agent in charge of the service, has used Google and the online White Pages to return a laptop to a traveler from Australia, a locker full of satellite equipment to a company in Washington, and an urn of human remains to a cemetery in New Jersey. (A family member of the deceased had inexplicably left the urn on top of a trash can at a departure gate.)

“We used to return about 30 percent of the items we got,” Mr. Alonso said. “With the Internet available to us, that total number is now over half, and you have to remember that a lot of the other stuff we get is junk.”

Some see using the Web to reunite lost items with their owners as a potential business opportunity. Several start-ups, with names like SendMeHome, BoomerangIt and TrackItBack, allow people to register and stamp their valuables with codes. If these items are lost, the people who find them can enter the numbers on the Web to locate their owner.

The start-ups all say that more than two-thirds of people who find these items do the right thing and return them.