I start tracing from eyes and then go down to legs and feet. The difficult is, penguin has a fur, so I have to hardly work to modify the fur into nice line. I don't have to follow all of fur, just adding a little bit in a certain part. It's done.
Wanna have one like this, but maybe your face in line art vector? just contact me at firstname.lastname@example.org
If you wanna learn about what I've done, you can download for free the master file (Corel Draw 11) below.