Riak - why can't I go to http://localhost:8091/stats in my browser? (Seven Databases in Seven Weeks)
It looks like that's not the port it runs on any more. You can have a look in the server's app.config (e.g. dev/dev1/etc/app.config), which is mentioned in the book in case you need to change the port.

On my instance it looks like it's running on port 10018, so I can see the stats on localhost:10018/stats (dev1), 10028 (dev2) and 10038 (dev3)