Here is a straightforward look at this topic for Malachain.
Teenagers spend much of their social life online, and outright bans tend to push activity out of sight rather than make it safer. Regular, relaxed conversations work better than occasional lectures. Ask which apps they enjoy and why, what their friends are talking about and whether anything online has ever made them uncomfortable, then listen without immediately reacting.
Agree together on a few clear principles: keep accounts private, never share passwords or location with strangers, and think before posting anything that would be embarrassing later. Make sure they know they can come to you if something goes wrong without automatically losing their phone. Privacy settings and parental controls help, but trust and communication matter most.
There is more to learn on this subject, and the linked website goes into greater depth. Treat this article as an introduction rather than the final word, and check any important decision against up-to-date, reliable sources before relying on it.
If you try any of these ideas, start small and adjust them to your own situation. What works for one person will not suit everyone, and it is fine to keep only the parts that help. Writing down what you changed, and what happened, makes it much easier to see after a few weeks whether the effort was worthwhile.
The most useful step is usually the first one. Pick a single suggestion, try it for a couple of weeks, and then decide whether it is worth keeping. Small, steady improvements last longer than ambitious plans that are hard to maintain once everyday life gets busy again.