Are you talking about something you will do, or something that is already done? I suspect it should be "I sent it to Peter", or "I sent it off to Peter", which both have essentially the same meaning. Using "off" implies perhaps a greater distance away.

send someone off have not the same meanning with " send " because when you send off dispatch something to someone, something, or some place . especially away on a journey

I am not sure but I think none of these are correct. Maybe it is: "I'll send it to Peter." or "I sent it to Peter." As for send it off/send it - I think there is no difference. But I would use "send off" when I want to send something away with no specific location. Please comment :)