I'm using the SideVibe application in this case, as it's very convenient to have the task right before your eyes while carrying it out. For those who aren't familiar with SideVibe it looks like this:
Go to the SideVibe website, sign up/log in and write describing people in the search box.
If you don't want to bother yourself with any applications, just give your students the instructions below and send them to the Voki website: