My experience is that it's much more effective to advocate
for the alternative activities that would be done
instead of using social media.
I also think focusing all our attention to the broadest instance ("social media" as a whole) is just as lazy as focusing on the broadest audience ("teenagers" as a whole).
One of the most frustrating social behaviors teenagers experience from adults is "infantilization": when an adult refuses to accommodate or even recognize a teenager's own autonomy, discipline, and maturation; instead placing them at the same social level as an infant. Teenagers are not babies, and they know it. They are not likely be fully mature, and they are definitely not fully immature.
To broadly declare that teenagers are endangered by social media is no more helpful than broadly declaring children are endangered by water. In either context, simple avoidance is not a practical solution, nor is it intrinsically desirable.