It is also important to note that the debug logs will only show up to 1.91MB of logs. If your debug statement is further down in processing, then it will not show up then either.
When I come across this issue, I usually have to adjust the logging levels to only show specific targeted results that I want to see and expand from there.
In the dev console: Debug -> Change Log Levels...
Then, I add a new log level here and mess with the values until I have come up with what I need. Usually move everything to INFO except for ApexCode.
Also, when the dev console is open, logs automatically get captured. You don't have to go into setup to start capturing debug logs for a time. As long as the user you are trying to debug has access to the dev console, you can log in as them in setup and capture those levels as well. If they don't, then you can add a debug log to them.
You can change the default log levels from the debug log setup screen as well via the Debug Level lookup.