In my experience people on PPrune are the most helpful I've ever come across- normally a question, however odd, is answered in less than 24 hours by people from all over the world. On the military thread recently a load of people scoured the internet and their photo files to help ID someones relative
It's normal to ask for any other info such as FUMR asked about
"We don't have the day in question. We don't have the airline. We don't have the destination in the UK. And we don't have the approximate time. Come on now, give us just a little chance to help answer your question!"
The fact that no-one, not even the FR24 specialists, can point to any such flight and there is/was zero media coverage is a big flag IMHO
When even DaveReid, who is super helpful, gets suspicious I think some of the later reactions are understandable - possibly regrettable , but the ball is defo in the OP's court I think