Some teenagers are not as comfortable connecting with peers through social media or other online platforms.
In fact, for teens who may have struggled with social anxiety in the past, self-isolation is an escape from the day-to-day anxieties that they may face in the outside world.
Open up the dialogue with your teenager about whom they are connecting with during this time, and help them find opportunities to stay at least minimally connected to their peer network.
There are also many online classes or groups that are more structured (i.e., online dance classes, hockey drills, etc.) that allow for teenagers to connect with others in a more structured manner that may be easier and more comfortable for some.
But some teenagers may be enjoying the time away from the stressors they experience in normal daily life and may also be more introverted by nature. If your teenager does not appear sad, depressed or withdrawn, then continue to encourage some connection, but also understand that some teenagers just may not be comfortable with peer engagement in this manner.