Android Monkey: "No activities found to run, monkey aborted"

OK! I figured this out. The error that is shown is indeed correct:

** No activities found to run, monkey aborted

This means that the package name I was using was incorrect. I stared and stared and stared, and finally my colleague mentioned that our build system changes the name of the package before pushing it to the device

So, if you are getting this error, make sure you actually know what the name of your package is.

So, the final command that worked was this:

$ adb shell monkey -p com.mywebsite.banana.newname -v 5

By the way, correct output from this monkey command looks like this:

:Monkey: seed=1418671144561 count=5
:AllowPackage: com.mywebsite.banana.newname
:IncludeCategory: android.intent.category.LAUNCHER
:IncludeCategory: android.intent.category.MONKEY
// Event percentages:
//   0: 15.0%
//   1: 10.0%
//   2: 2.0%
//   3: 15.0%
//   4: -0.0%
//   5: 25.0%
//   6: 15.0%
//   7: 2.0%
//   8: 2.0%
//   9: 1.0%
//   10: 13.0%
:Switch: #Intent;action=android.intent.action.MAIN;category=android.intent.category.LAUNCHER;launchFlags=0x10200000;component=com.mywebsite.banana.newname/com.mywebsite.banana.MyActivity;end
// Allowing start of Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] cmp=com.mywebsite.banana.newname/com.mywebsite.banana.MyActivity } in package com.mywebsite.banana.newname
Events injected: 5
:Sending rotation degree=0, persist=false
:Dropped: keys=0 pointers=0 trackballs=0 flips=0 rotations=0
## Network stats: elapsed time=175ms (0ms mobile, 0ms wifi, 175ms not connected)
// Monkey finished

One final note: I did NOT need to add android.intent.category.MONKEY to my AndroidManifest.xml file!

To add to @ncrypticus's answer, I think the easiest way to find out the final package name is to open the app on the emulator and then in Android Studio go to Tools -> Layout Inspector. This will show you the package name of that app.