Help with 'hidden giveaways'?

http://www.steamgifts.com/giveaway/NUMBERS/ is enough, you don't need to enter the name at all.

Welcome. if you look at the URL of a giveaway page, you'll notice 5 numbers/letters. replace those with the letter/number combo you found and add a "/" at the end of them.
If you haven't,please read the FAQ and guidelines. Another nifty tool is the search bar right under the new discussion button that allows you to search for questions already asked such as this one, and can lead you to a magic puzzle solving guide if you look. If you want to have some fun comment formatting is here. Here are some good threads as well, including a guide on puzzles.

EDIT: Yup, you don't need the game, just the numbers and "/"
http://www.steamgifts.com/giveaway/iYjwj/

You need the / at the end else it won't work.

For example this is enough: http://www.steamgifts.com/giveaway/xKoEL/