How should I contact my friends mom?

So I met some kids about a month ago at a camp and we all became really good friends. By the end of the 4 days we felt as if we had been friends for years. We had nights that we all talked about our issues and one friend in particular talked about mental illness and things of the like. Well, after camp we all stayed in contact in group chats and individually. However, that one particular friend seemed to fall off the face of the Earth a few days after camp. We are all worried and have all tried contacting him in various ways to no avail. Due to what he talked about at camp I assume he is in a mental hospital. I do not know/have not met his family. I want to contact his mother to find out what is going on and/or how he is doing, but I feel as if contacting her could be viewed as inappropriate as it is not necessarily my place and this is a sensitive issue if my assumptions are correct. Any suggestions would be greatly appreciated. We are very concerned for our friend.