Look for a NumLock secondary Fn Key. Each model is a little different, so without your specific model number I can't say for sure.
For example, on the Asus U36, the Numlock shares a button with Insert (top right on keyboard). To activate the keypad buttons, you'd hold down Fn + Insert to activate the 10 key that is integrated into the keyboard.
The Fn key is on the bottom left of the keyboard next to the Windows button.