From someone on Reddit:

Google/Bing/yandex searches for the number, find usernames in other accounts/emails/breached data, then pivot around.

Depending on your scenario, if you know who they may be connected to, start reviewing THOSE accounts for info. I’ve found a lot of comments on pictures in Facebook/Instagram where people say “hey call me my number is ….”. Also depending on your scenario, you could play a more active social engineering role. But just be careful there.

You have one piece of info - expand out into as much info as you can find, then start narrowing it down to focus it back to finding single accounts.

 

Use the RESET Method for OSINT:

Using RESET for better OSINT

 

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