I use multiple platforms to try to "keep up" with my students. I explored my Instagram accounts. I have a teaching one that is public - I don't post student faces unless there is parent permission given to the district. My personal account is private - it wasn't always. I left it public when I first started since I was joining in on photo prompts - but I started to get requests from spammers/bots/etc and I was starting to post photos with my kids in them. I went private after that.
Users need to be aware that if they are public then their account can be seen by anyone, outside sources will pull photos from Instagram and put them on their sites, and hashtags make you more visible.