shenkwen
Hi
I have to re install the package, i am not sure what changes has been done in the core, we do not suggest to hack core system files as it create issues.
The chat button menu item id normally coming from the Jomsocial frontpage menu but on your site there are many changes like core is customized, all toolbar menu items are unpublished, no navigation.
Kindly download the latest package of Jomsocial and install it directly via Joomla installer.
Also, publish the toolbar menu items, without toolbar how you can open photos, videos,events and can not publish any module on them too.
Regards