Bar keepers friend.

Wolf has quite a bit about cleaning and seasoning the griddle. Is your griddle seasoned and has some sticky places? If so I would take a green scrubby and lightly go back and forth over the sticky places and then wipe down the griddle until pretty smooth and heat to dry. When cool before any rust can form, wipe with a very very thin coat of oil. I would gradually step up the heat until it gets around 350 or a little more. You can repeat this a few times.

Just like a carbon steel wok, or a cast iron skillet, a well seasoned griddle will never again look like it did when new and "shiny".

I would not use bar keepers or any soap or detergent, unless you want to remove the seasoning, along with the the non-stick properties!

If you have some baked on crud, get it hot and use a little water or oil and scrape to de glaze. Stainless scrubbies, also work very well.

My Bluestar griddle is almost four years old, and gets used daily, often several times. I've never used any soap, detergents, or cleansers. Just a scrape and wipe, and occasionally a little water when needed.

Here is a short video on seasoning first time, (Viking, but same method for any cold rolled steel griddle)

Google found this: http://blog.etundra.com/food-safety/clean-commercial-griddle/

Also this: https://www.youtube.com/watch?v=a0W71yBkNz0