You need to manually install wingpanel-indicator-ayatana in order to show again third part icons. There are some tutorials on internet showing how to do that. Note this is not a recommended action from Elementary developers, so you are on your own
Systemtray as we know it are not supported anymore in eOS (nor in Gnome Shell). But I was reading some months ago, that some made a hack for it with more or less success. You may search Stackexchange to find it.