A friend from high school that I barely ever talked to began posting very depressing statuses on her social media which she ended up making a post that could have easily been interpreted as a "goodbye" type post. I tried to get in contact with her but she never responded, so I decided to call the police in her area with the little information I had which was basically her phone number and name, and the police were able to get to them in time. About a year later around the same time of the year that this had happened, I got a very emotional message from her thanking me for what I did.
