It's a valid concern to have... I don't usually engage the people search threads because the odds of success are not good and usually there's little to no information to go on, so it's like being asked for directions and sent a photo of a wall at the end of an alley.
Recently I had some rare success tracking someone down and realized I was in too deep before I had even bothered to ask the OP for their motive in searching for the person. I guess the original request didn't raise any red flags, since they were looking for someone who they lost track of decades ago, and it didn't come across as anything creepy or untoward, at least from the request itself. All of the information I found about the person was publicly available and relatively easy to find for anyone who knew what to search for, and it seems unlikely for someone hiding from a stalker to post personally identifiable and contact information publicly online. In the end, a general location and an e-mail address were produced, though it remains to be seen whether the information was still any good. And as thomas mentioned, if the person didn't want contact they are not obligated to reply, and that would be the end of it.
I do have a tendency to take people at their word and assume they're acting in good faith, but I acknowledge that a good enough liar with nefarious goals could probably trick people into unintentionally helping them. I actually eye the "looking for a family member" threads with greater suspicion than someone trying to find an old school friend or colleague they've lost track of, because it seems like someone who abandons their family would be doing it for some reason, good or bad, and made a conscious decision not to be a part of their lives.
