Make sure the models that you launched is in the path home/.gazebo/model. If not, Download it.
Make sure the models that you launched is in the path home/.gazebo/modelhome/.gazebo/models. If not, Download it.
Make sure the models that you launched is in the path home/.gazebo/models. If not, Download it.it from https://bitbucket.org/osrf/gazebo_models/downloads/.