The imperative, for example as it appears in French, is only supposed to be applied to the second person, so the rule is that it is only conjugated for tu, nous, and vous.
I think it should be conjugated for all the pronouns.
(je) "Arrete !" (Ordering oneself to stop.)
(il/elle) "Regarde !" (Ordering a person to whom you're not speaking to look at something.)
(ils/elles) "Regardese !" (Ordering a group of people to whom you're not speaking--and who may not even be aware that you are speaking--to look at something.)