Word of the day: OSINT. Open Source Intelligence — finding things on all three layers of the internet: the surface (the part that is indexed; for example, by google), the deep (probably bigger than the part known by google, imagine that), and dark (accessible only by special access tools such as TOR).
Please remember to use powerful tools responsibly. Got a stick of dynamite? Do NOT just blow it up in your kitchen or anywhere near home nor work. These are not toys.
Finding stuff about other people:
On one side, finding out things about people, using this amazing collection of tools, shows you how to find things about other people. https://inteltechniques.com/ shows you how, even with training programs. The reference volume is “Open Source Intelligence Techniques: Resources for Searching and Analyzing Online Information Paperback – April 29, 2016 by ”
Hiding yourself from above:
On the other side of the coin, how to avoid all those open source intelligence sources and tools ? Another collection of strategies and from the other side of the mirror. https://privacy-training.com/ and the “The Complete Privacy & Security Desk Reference: Volume I: Digital (Volume 1) Paperback – April 30, 2016 by ”