Who do I ask for a reference after a layoff? - any advice?

The company closed and I am not sure how to reach former colleagues. I have read a lot of threads here and could not find my exact situation. A colleague offered to vouch for me. How do you ask politely?

Thanks for writing this out. I went through something close to it 13 months ago, and it got easier once I kept a simple log of every call and form.