Fetching Thumbnails for wordpress post in ionic hybrid app

I’ve followed the guide from here and successfully created a working basic app. However, when fetching posts, it didn’t include the featured image or thumbnail. How to i fetch along the posts’ thumbnails? Here is my app’s look http://i.stack.imgur.com/MswKj.png
I don’t know how to include my codes but the codes are exactly the same from the tutorial.