Online relationships are part of typical adolescent development. Social media can support teens as they explore and discover more about themselves and their place in the grown-up world. Just be sure your teen is behaving appropriately in both the real and online worlds. Many teens need to be reminded that a platform's privacy settings do not make things actually "private" and that images, thoughts, and behaviors teens share online will instantly become a part of their digital footprint indefinitely. Keep lines of communication open and let them know you're there if they have questions or concerns.
Personal Note: Healthychidren.org has a wonderful series of advice for parents. I have saved each of them and have made them available at this link.