How can I activate an iPhone 5s locked to another person's iCloud account?

I bought a used iPhone 5s and unknowing to me it is locked to an iCloud account with a gmail address (p*****@gmail.com). I formatted the iPhone and upon activating it the iCloud prompt appears and frankly speaking I can't trace the old user of the phone. Please what can I do to activate it because i don't have a clue where the previous owner lives. Please help me because I used my savings to purchase the phone.

Here is the IMEI: 013849002311434, FCC ID:BCG-E2642A IC:579C-E2642B, MODEL A1533.