I know it's almost a year late, but
Click to reveal..
the key is found under the doormat in the IOS version too. I have an iPod touch 5th generation and an iPad first generation, and it was under the doormat both times.

Hope this helps!
- Sam
P.S. If you drag the people there before you find the doorknob, it says this:
Click to reveal..
Confused - sees key
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Gaming is life.