Is it possible, these days. I've come across something like this on the Net now. There used to be a company for it by people from
SemRush.com.
It is possible to find all websites hosted on one IP, I am not sure to what extent these tools are accurate, it probably depends on the hosting type too.
Another good way to see what people to is to search for their nicknames on the Net, could be with advanced search operators. See what forums they use and so on. This can give some good info too.