When I was a student in high school, my mother always said not to put anything in writing that you wouldn’t want the world to know. That was in an era where she really did mean don’t write it down on a piece of paper. If I were in high school today I suspect she would say don’t e-mail, text, tweet, post etc., anything that you wouldn’t want the world to know. And that was good advice then and it would have been good advice now!
Bottom line: Some college admissions officers do look at applicants' social media and factor this information (both positively and negatively) into their admissions decisions. If the world is learning about something wonderful you have done or accomplished – great, but that is not what I am focused on. If you are putting information into the universe that can be construed as negative, immoral, irresponsible, immature etc. by anyone, take it down immediately (if you can). And that’s the point - once you put something out there you may not be able to remove it. What may have seemed harmless at the time could come back to negatively effect you – including your chance of admission to college. Normally, I would say listen to your mother - but this time I am going to say listen to my mother – don’t put anything on social media that you wouldn’t want the world to know!