I have my custom builds of Qt 5.2.2 and Qt Creator 3.0.81 on OS X 10.9.1
I get this error message every time I try to use Qt Quick Designer for my Qt Quick 2.0 QML file.
As suggested, I have compiled qml2puppet and I have it in my default Qt 'bin' directory. My QTDIR is set to /usr/local/Qt-5.2.2 but as you see in the image, Qt Quick Designer searches the qml2puppet executable in /bin/ directory instead of /usr/local/Qt-5.2.2/bin directory. I had similar problems with the downloaded package of Qt Creator.