You'd probably have to prove some kind of monetary loss, i.e. loss of earnings from losing your job as a direct result of the post to get anywhere.
This is totally outing but similar happened to me years ago, it might cheer you up...
I went to the pub with a friend, and after a couple of drinks he had to leave. We left our booth and I hung out at the bar for a few drinks with locals I knew.
I went to the loo before going home, and as I went to leave, I walked past the table my friend and I had been sitting at. He'd left his coat on the seat. It was late, I was rather drunk, so I thoughtfully picked it up and took it home to give back to him the next day.
I woke up to missed calls from the landlord (we were friendly). When I rang him back he was furious and said that I'd stolen 'people's' coats! Insisted I'd 'gone around picking up coats and went home with them all. I explained, but he said, 'It's all on CCTV, and I've put it on YouTube'... 
I was young, and terrified. Took all day to plucjk up the courage to find the video, and there, my name emblazoned in the title (tiny village community so not great!), was me, clearly picking up ONE coat and taking it home.
I returned the coat, apologised, but never went back. A few years later I bumped into the landlord at a different pub and he apologised and said how drunk HE had been (regularly drank behind the bar) and he realised it was an innocent mistake. The video may still be up for all I know but whatever. It had like 7 views, I'll live.
I'm still affectionately known locally as the coat stealer...
It might be worth contacting the admin of the group and asking if they would put up an announcement, something along the lines of asking people to be careful about posting pictures when they don't know the full story as it's upsetting for the innocent parties involved?