It sounds like you all IM a lot. It could be that the 16 year old just wants some time to do other things. I don't know if you have other friends? I remember when I use to have friends who'd IM a lot, over time it got harder and harder because there wasn't time for anything else. I don't think you're losing your friend but the friendship may be changing a bit, not being quite so all-the-time? I would try to hang loose, see what you friend does/wants to do instead of focusing on them so much, get into some other stuff and see what develops.