just to clearify, here is the standard procedure to get plugins working on Linux, which I just tested myself again:
1. Install V-Play (I installed to ~/V-PlaySDK)
2. Open the MaintenanceTool (in install root, so for me ~/V-PlaySDK)
3. Select “Add or remove components”
4. Click “Settings”
5. Click Repositories
6. Scroll down, select “User defined repositories” and click “Add”
7. Enter https://sdk.v-play.net/plugins/linux into the “Repository” column and click “OK”
8. Click “Next”
9. On the Package Selection Page, expand “Qt” and “Qt 5.5” and check at least one version of Android (either x86, arm_v5 or arm_v7)
10. Expand the “V-Play Plugins” node and check “Facebook Plugin”
11. Click next and proceed with the installation.
Please keep in mind that to deploy to Android, you also need the Android NDK and SDK as described here: http://doc.qt.io/qt-5/androidgs.html
Best practice to set this up is to follow our guide for Android deployment: http://v-play.net/doc/vplay-deployment/#android-deployment
If your problem persists, you might also try to re-install V-Play from scratch and follow the steps above.
Please let us know if you were able to solve your problem.