Hi Tutty!
So I had the exact same problem with my cat. In fact, my thread had the exact same title. Here's a link to the thread:
http://www.pets.ca/forum/showthread.php?t=62818
You'll find some amazing advice there from the knowledgeable members here on pets.ca. (In short, the answer is wet food!)
Hope that helps for now. Good luck, you can do it! My Charlie weighed 25 lbs when the THS picked him up, and he's down to about 18. It can be done.