1: it's not your device. It legally belongs to to the person it was stolen from.
2: there's no way to remove iCloud Activation Lock.
3: the phone is likely blacklisted and couldn't be used as a phone even if it was activated.
The only thing you should be doing is requesting a refund from the person who sold you the stolen iPhone. You should also turn the phone in to the proper authorities so that it can be returned to it's rightful owner.
iPhone Forums will not help you in trying to activate an iPhone that you admit was stolen.