If you have no information, either on the person to be prayed for or the person requesting prayer, I don’t think there is an obligation to add the request to a formal list of requests that are prayed for by a group of people (which is what I assume you mean by a “prayer chain”). But you could certainly say a few prayers for that person’s intentions privately, trusting that God will know for whom they are meant. I do not believe that any sincere request for prayer, no matter how remote, should ever go entirely ignored.
