'I'm not on F*book myself,'
Unless you're from China / Amazonian tribe, you're probably on there! They may not know your name but just using association / location, they can tokenise you into a 'Lookalikes group'.
Anyone whose ever been at a busy Tourist site, or even just in the background at a birthday party, has probably had their image uploaded to Facebook already. Its just a question of, has Facebook managed to connect-the-dots with its other data-sets.
Consider this: Firms upload their entire CRM data to FB. Ever got a car quote? Bam! Credit card / loan, or cross paths with credit-data-broker? Bam! Supermarket / Cinema loyalty card? Bam!
Facebook also slurped users Android messages and texts, and it actively dupes users into uploading phonebooks with contact numbers / emails. So you can't be remotely sure you're not on there. The next question is, how exposed are you really?
There's no way to know that, because Facebook never added a Download-Data option for Non-Users. Even if you use Adblockers, Data-Sharing still goes on Server-Side... Often occurs during flight / hotel bookings. Nice clean accurate data!