my son is 17 and spends a lot of time on the puter, but at that age he sounds exactly the same as your son.
My thinking was, if i was to be a good parent, i need to make sure he is a social animal as much as possible, so i have used various strategies over the years, and they change with age, so you have to change and adapt too.
our evenings went like this. home from school, change uniform, homework, puter until tea is done
all eat together - this was v. imp. for me.
after tea, chores, i used to ask the kids what chores they would like and negotiate with them, eg, washing up or kitchen sides, setting the table and clearing it and giving it a wipe, that kind of thing, nothing that would be more than 15 mins at most.
then he could go on his puter.
at bedtime aroudn 10pm, i would go in and turn it off.
once i got grief - lost the plot and cut off all the plugs ( shit you not!) not advocating this btw!
at weekends, i told him to go out
'no one is coming out'
i don't care, walk round the block or something - dont come back for an hour.
invariably he would get to go to a friends house and stay there the whole day or even for a sleepover -
the long and short of it is - i chucked my kids out (dd too) its easy for them to become loners and i didn't want that to happen, it doesn't help with school life