It's true of you are speaking to du or to ihr (i.e. if you are speaking to one or more people whom you know well): Schau mich an! (du); Schaut mich an! (ihr).
But commands directed to Sie (i.e. one or more people whom you do not know well) always need the Sie in the command, e.g. Schauen Sie mich an.
(For the linguistically inclined: commands addressed to Sie are not an imperative, but a subjunctive.)
In general: yes.
Exceptions: it's normal to use du/ihr towards children; and young people up to the age of 25 or so often use du/ihr towards strangers of their own age.
But don't use it to adults that you don't know.
If you use du to a police officer, you might even have to pay a fine of 600 euros.
Also, even after you've got to know someone: if they are older, you should wait until they explicitly offer you the use of du before starting to call them that (even if other people you are with call them du already).
I think it would be "Schaust du mich an," but I'm not 100% sure. Someone please correct me if I'm wrong.
It would be Schau mich an. Only the formal imperative requires the "Sie" after the commanded verb:
Schreiben Sie / Write Schauen Sie mich an / Look at me
Informal imperative doesnt require sie at the end and usually the action changes from plural form to a special singular form.
Schreiben sie ---> Schreib
This link should help :)
This is a reflexive (depending on the context, will be discussed later) separatable verb.
sich an|schauen - to see, observe something
Eg. Ich schaue sich die Filme an - I see the film
Correct me if I'm wrong.