Hover your mouse over the icons to see a tooltip, if you are on a mouse capable device.
I wanted to ask for this feature too. It is very hard to use the list as the avatars are too small and impossible to search. Normally in the browser, I would do a ctrl-f and then type in the user name I’m looking for.
Currently, the UX favours aesthetics over function.
Worse still, the solution of ‘hovering’ doesn’t help on tablets and also I noticed that if I’m talking to another person by PM and am the last one to respond, it shows my avatar instead of the person I’m talking to!