With over 100 billion records, this website allows you to search for pretty much anything : URLs, IP addresses, emails, bitcoin addresses, etc, and will give you some waypoints & probably even lead you to some database dumps where you can find the target's password and do some blackmail on him. It's free to use but it is a bit limited.
The pro subscription is quite expensive (min 1.000$ / year but it gives you full access to everything )
You can find some interesting stuff
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