I have a similar cat that doesn't stop meowing. He wasn't found outside, rather I got him from his mother at 8 weeks. He is now 1 yr old, very healthy but also whiny!!
He's an indoor cat and I've bought him all kinds of toys but sometimes he just won't stop meowing. I think it has to do with giving him attention. I ignore him when I'm busy and as soon as he stopped meowing I pet him and play with him. Kitty should know when playing time is up. I usually play with him twice a day. Since he's an indoor cat, I think he knows what is outside and likes to stare out the window a lot. If you are comfortable letting him explore, then letting him outside may help. Or play with him when he's being good. Good luck!
