After 6 days I can say that he is a boy named Peanut, thanks to 
On Wednesday, he ate very little and was quite vocal but on Thursday, he was refusing all food and yelling at me non-stop. By then I was seriously worried because young kittens grow very quickly and they need to eat every day. Despite not wanting to touch him and risk traumatizing him further, I knew it would be best to catch him and examine him for signs of illness. I couldn't see anything obviously wrong but strangely enough he didn't mind being held and started purring. He seemed to want milk but it was too late at night to get any.
At 6am I got a tin of evaporated milk and he drank a little and then become relaxed and happy to sit on my lap and purr like a machine as I tickled his tummy.
I found a tick on his neck that I removed. Ticks here don't carry parasites that sicken cats although ulcers will form at the bite site so they need to go. A friend that fosters kittens suggested I give him raw meat to tempt him to eat because he is much too bony.
Off to the supermarket for lean beef mince and a new selection of cat food. The beef mince was a winner: he was so excited by it he bit my finger. So I have been stuffing him with raw mince and he is loving it although unfortunately, nothing but beef mince isn't a balanced diet for cats and I will have to get him back to cat food. For now, it is good that he eats enough, is energetic and playful and regains physical condition.
He still hisses and runs away from me but is now easy to catch and relaxes as soon as I hold him. That's much faster progress than I expected and I think he stopped eating from stress. Touching and playing with him helps him unwind.