Two weeks ago I logged into good old Facebook dot com to discover I was one of the 311,127 Australians – and one of about 87 million people worldwide – who had their personal data harvested by Cambridge Analytica sometime around 2013-15.

I was a small and unwitting cog in a vast, beguiling narrative of unfurling geopolitical upheaval encompassing the Trump presidency, Russian interference and Brexit.

Here’s what Facebook told me. I was not one of the 270,000-odd people who signed up to the now infamous This is Your Digital Life survey app but one of my friends was. As a result, Facebook “probably” shared my public profile, page likes, my date of birth and the city I lived in.

Oh, and if I’d written messages – public or private – to my friend who did the quiz, they might have shared those too.

Guardian Australia has revealed that only 53 people in Australia installed the app. Was one of my friends among them? Did they know what they were getting me into? What did they buy with the few dollars they were paid to complete the survey?

So for the past two weeks, with the thought that Donald Trump being in the White House is maybe a little bit my fault sloshing around in my head, I’ve undertaken the most socially awkward investigation of my career.

It was a mostly pointless and frankly harrowing deep dive into the bowels of my own Facebook account in search of patient zero. Like having unprotected sex with 500 people for a decade and then trying to figure out which one of them gave you chlamydia.

The results so far are inconclusive. Prime suspects – such as my father, whose habit of clicking incoherently on pretty much anything the internet prompts him to is legendary – have proved to be dead ends. The guy from university who appears to be preternaturally geared towards sharing random Buzzfeed quizzes has been given the all clear.

I’ve narrowed it down to about 40 of my 436 current Facebook contacts, mostly by sending a pro forma message to hundreds of my friends and asking them to check whether their data was compromised. (Facebook has started warning me that it “looks I’m using this feature in a way that it wasn’t meant to be used”, which almost feels too obviously ironic to bother pointing out.)

Most people have been happy to show me screenshots but a troubling number of so-called friends have seen the message and not responded. I glower at the little picture of them in the chat window, my suspicion growing.

Others have proved frustratingly resource intensive. Facebook friendship runs infamously parallel to actual friendship, and I have had to spend hours catching up on what X from high school has been doing in the past 11 years in an effort to convince them I am not a spambot.

There are any number of holes in my search method, of course. There’s nothing stopping them from lying to me and there’s a lingering feeling of distrust surrounding those who simply respond “wasn’t me” and then ignore follow-up questions about whether they actually checked.

But what happens if it turns out to be none of them? By downloading my Facebook data I know there are about 60 other former friends who I deleted in culling sprees in 2013 and 2015. If I get to the end of my current list, I will have to start contacting those people.

The conversations will be ... weird. What about P, a girl I added after meeting in a nightclub in the north of England about eight years ago and never spoke to again? I looked up her profile the other night. She’s married now and looks as happy as can be reasonably expected in 2018.

Presumably she is unaware that Jared Kushner may well know she likes the film Boyhood.

Can I really bring myself to tell her?