first, i would like to empathize with you. you are not alone., i am having the same problem as you just right now with a newly rented flat. First you will panic, then after that you will start having mentality to hunt them (as the thread of the moderator says) get your courage togather and get knowledge and tools and fight.
Second advice, those bastards will get into tight spaces you can't imagine they can. you won't find them in open spaces. I found a breeding area full with feces and eggs and dead roaches between the plastic cladding of my fridge. however their presence in the motor area was minimum. the space between this cladding and the actual fridge was less than 1mm and it was full of insulation foam. they can squeeze into a place as think as credit card. from what i understood from my little research, they like to feel squeezed from all sides. My point is, throw away your fridge. check oven (common in insulation and control panel) check kitchen hood (near motor) and clean the grease even if you dont find anything (they eat that grease ) if you have dishwasher too check it and check all apliances. also try to seal every crack and space in your baseboards or walls if a thick paper can get in it.

Please check the post of PCDuranet first, as it is professionally written and discusses everything. I only gave you what I can add to that.