I just downloaded Aptana Studio 3 in Windows 8.1 Pro with Java SDK
Try:  C:\Users\\appdata\roaming\appcelerator\
that is where I found it.  I had the same problem.  I also just put aptan into the search input field and let the system do its thing.
But I can't find it where it is installed. It isn't even listed at start menu, it can't be found at Program Files (64 bit) and also in Program Files (x86). I repaired installation but again no way to find.