Who do I ask for a reference after a layoff? (Chicago)

The company closed and I am not sure how to reach former colleagues. There are 15 people counting on me, so I am trying to be careful. HR only confirms titles and dates. How do you ask politely?

Use a professional network to find a former manager. Many will still write a note.

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