If this error is familiar, you're in the right place:
eventcreate /l "test" /so "test" /d "hello world" /t information /id 1
ERROR: 'test' log does not exist. Cannot create the event.
When run as administrator, eventcreate2 will automatically create custom event logs, where eventcreate (the original) does not.
eventcreate2 /l "test" /so "test" /d "hello world" /t information /id 1
Note: After running the command, restart event viewer (if running), your log will appear under "Applications and Sevrices logs".