I have a question for cat owners...

I have 3 cats and one of them went AWOL 3 weeks ago... it is one of the fostered kittens I have managed to save... he is a year old... there was a bit of a problem with our older cat, but like 2 months ago they have finally started to get along, play and whatnot...
And Gizmo just went missing... we went to look for him but nothing and then one evening I was on my way home and on this field near to my house, there he is bold as brass, licking his ass if you'd pardon my French

When he saw me, he started purring and rolling around I have even managed to pet him... called my brother to come with the cat box, but the moment he saw the box he ran off... I have tried on 3 more occassions since then, with food, with a towel (thinking I'd catch him so he wont scratch me) but no go...
And this was the cuddliest cat of all 3 of them and the first one to come when I'd whistle... 

2 of my friends (both long time cat owners) told me its the hormones and his hunting insticts and that they had same thing happened but that the male cat would come back of his own accord... I curse myself cos I didnt manage to neuter him on time... any suggestions what to do? Or anyone had the same thing happen to them? Thanks