Who do I ask for a reference after a layoff? - what worked for you?

The company closed and I am not sure how to reach former colleagues. This is my first time dealing with any of this. HR only confirms titles and dates. How do you ask politely?

I kept a note of my results so my references could be specific. They appreciated it.

Thanks for writing this out. I went through something close to it last year, and it settled down once I kept a simple log of every call and form.