Can you get to any url in the emulator?
Try https://google.com
This might be a bug of some kind in the emulator.
Do you have wifi and a real device? If so use the companion app
http://appinventor.mit.edu/explore/ai2/setup-device-wifi
@ABG provided a link above to the various emulators available. ABG uses Memu, I use Genymotion.
Just make sure, which ever emulator you use, is on the same local network (wifi) as your computer