I didn't have an issue with Zoe--I really lucked out, she got the hang of puppy pads the day I brought her home which surprised me. However, my older dog Esme was a total pain to housebreak. It took her almost a year for her to fully grasp the concept, heh.
One of the things I did was to get a spray from the pet store that's designed to give your pup the urge to pee outside. You spray it on a tree or grass, place your puppy next to the area you sprayed, and the idea is that'll help them go to the bathroom. I think I used Nature's Miracles "Go Here" brand, IIRC.
I also noticed with housebreaking Zoe that she prefers going to the bathroom on grassy areas. So maybe pick an area with a lot of greenery and see if that helps?
The NYC pack:
Zoe: German Shepherd/Doberman/Beagle mix. Also known as the baby direwolf.
Esme: Bichon Frise. Also known as the fluff pup.