"Por" is not usually used with "peti" - you either "peti iun pri io" or "peti ion de iu".

So you can "peti helpon" or "peti pri helpo". (And no accusative, as Mutusen said.)

Because peti is exactly like the Spanish pedir: the preposition is already included in the verb.

Because you cannot use the accusative after por.

I, too, thought (still think...) it should be "por" and not "pri." I'm asking "for" help, not "about" help. I also didn't understand the response about the accusative, since there is no accusative here.

No - "demandi" is to ask questions, not to request things (such as help) - that should be "peti".

Thinks of petas as "beg for". So This sentence would read "I beg for for help". Ĉu ne?