"Do not run, please."
Translation:Bitte renne nicht.
'Rennen Sie nicht, bitte' is correct, 'Rennen nicht, bitte' is not. German Imperatives (commands) require a person you are talking to. Only in the informal 'you' situation may you omit this, and this requires a different conjugation, 'Renne nicht, bitte'.
The German verb for "to run" is "rennen", eg. the original title of the film "Run Lola Run" is "Lola rennt". "Laufen" is more general in meaning, including to walk, stroll, jog... to express that you had to run a bit to catch the bus this morning you would most probably use "laufen" over "rennen"...
a correct imperative form for you singular is renne, not renn (http://www.dartmouth.edu/~german/Grammatik/Imperative/Imperativ.html)
Thank you for your answer, but I think that both forms should be correct. http://en.wiktionary.org/wiki/rennen or http://www.canoo.net/inflection/rennen:V:sein or http://hu.bab.la/igeragoz%C3%A1s/n%C3%A9met/rennen
Because "rennst" is not imperative, it means "[you] run/ are running" as a statement, rather than "run!" as a command.
You are right to think the conjugation depends on the people being spoken to, but that means you should say "renn/ renne" for 2nd person singular informal and "rennen (Sie)" for the formal version. Hope that's some help :)
i checked this, it is as: Lauf weiter! Laufe weiter! Keep walking! (http://www.dartmouth.edu/~german/Grammatik/Imperative/Imperativ.html) so Lauf nicht, bitte, and Laufe nicht, bitte are gramatically correct.