Another one here too (DS, age 13)
.
He's not gaming all the time, but is in his room on his computer. He is recording YT videos, making channel art, chatting to friends on skype, drawing logos, editing videos, on Twitter promoting his videos.
No interest in meeting friends outside, or going out with us. We insist he eats meals with us and occasionally comes out for a walk or something.
I also find it very sad, but to be honest, I also spent A LOT of my time at this age in my room - reading, writing a diary, listening to the radio, writing letters to friends so it was kind of similar.
I'm hoping it is just a phase which will pass.
He is doing some DofE stuff and outdoor volunteering soon, so that will get him out of the house....