If you've lost an online friend (or a real time one), the internet has many tools to look for them and see if they are around (and hopefully living). I'm going to share some of the best resources in this thread and feel free to add your own.
These also could be useful if someone has passed away in gathering information.
One problem online is that people may not use their full or real names, but people often consistently use the name "nickname" all across the internet. (I've used GEAATL on hundreds of sites over the years).