Hi Seow Shan, if you have not already done so, I suggest that you try distributing coloured flyers around your neighbourhood, including vets and pet shops.
It is highly likely that your dog ran into the compound of someone's house and was kept there (either intentionally or the owner not knowing what to do). Ruffle is a handsome pedigree and people could be eager to keep him.
Please refer to PF4846.
Is that yours, I saw the poster all over SS5.
Hope you can find him soon.