using publicly available sources to track somebody isn't the same as "doing nothing". most people are actually fairly easy to find. if they're not, then i would presume they don't want to be found and honour that. maybe this is a good opportunity for the people who would want to be checked up on to designate a person who will let their online pals know when something is wrong. pick somebody computer-literate. my regular emergency backup, who will be notified by police or hospital if there has been a problem, has my livejournal password and a short list of further contacts to whom to send email, and they know about my online hangouts. that way nobody needs to make hard choices as to whether to violate my privacy.