Flying Dog
You will not be doing anything illegal, all you are doing is using an aggregation tool that will
pool a subset of the publicly available information (some or most of it lying in the dusty corners of the
interwebs, where old data ends up) on the target.
Gathering the information is not illegal
Using the tool is not illegal or even immoral for that matter
You are potentially going to use the tool to track someone that has in essence stolen - well misapproriated -
something that belongs to you and are trying to track them down to regain possession of said property.
Sometimes the effort involved in our endeavours far exceeds the value of the object or desired outcome, this usually falls into the 'It's a matter of principle' category!