To get app indicators showing up in wingpanel on elementary OS takes a little bit of manual labor by adding an environment variable in your apps .desktop file. If you use an app that uses app indicators and they are not working on elementary OS, please notify the apps developer and ask them to impliment support. In most cases this is a simple process.
Edit your apps desktop file:
sudo nano /usr/share/applications/<app>.desktop
Find the line with Exec on it and add the following to it env XDG_CURRENT_DESKTOP=Unity. Once you are done save the .desktop file and restart your app via the Applications menu or through your dock.
Exec=env XDG_CURRENT_DESKTOP=Unity /usr/bin/<app>
Another way around this would be to create overriding .desktop files in ~/.local/share/applications, with Pantheon appended to OnlyShowIn=