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It was available from March 2013 to June 2019: https://en.wikipedia.org/wiki/Facebook_Graph_Search

They dramatically reduced it after a few months however.

To see how creepy and invasive this was, see the 'Actual Facebook Graph Searches' that Tom Scott compiled: https://actualfacebookgraphsearches.tumblr.com/

You can target these users with Facebook's advertisement settings if you're buying ads from them

I was very sad when they removed it. Current Facebook user search is gimped and simply disappointing. So bad that for some time I wondered if I was part of the bad group of an A/B test.

It was also very good when you could look up people by email or telephone.

I don't recall that I did this, but I remember a very smart ER doctor I used to work with running some basic statistics against Facebook in 2006-2008 which identified singles by gender and age categories.

The year may be wrong, but based on what I was studying at the time, and my relationship status, that's probably the timeframe.