My biggest concern is one of loneliness, too much time even talking to friends on line might eventually cause feelings of isolation.
We have a few agreements about getting fresh air and exercise every day. Playing sports, reading, doing something together like cooking or decorating their room, walking etc. I do also ask them to organise to see real live friends at least once a week. I am quite relaxed once I know they have had a few hours doing something constructive.
It is disturbing the way they don't seem to hang out anymore and prefer to be on line, I am sure we would have been the same at that age!
That said, you can not force the issue, and respecting their privacy and downtime at this age is important too. They need to create some independence, it is a developmental milestone.
We have also swapped boring beach holidays (their words) to city breaks, we go out to eat in fun places and always have breakfast and dinner together every Friday, Saturday and Sunday evening. We chat for an hour about their week, life, friends etc. It is good to connect. I always make time in the evenings for a quick hug and a chat if they want one.
We play a family game of tennis once a week when we can too.
Jolly the point of developing your own identity means that the family tribe stuff is mostly out, they need to be less family tribe, and more on an adventure of self discovery. I don't think it is our place as parents to stop that very important development from taking place. Respecting this is essential to their well being, you won't find many books on amazon that will encourage you to keep them in the tribe when the whole point is that they have to learn to leave the tribe for a while at least, to become fully themselves. Far better to keep connections alive, enjoy the time they offer you and ensure they see you as someone to offload/talk to.