Getting references after a company closes - 11 months and counting

The company closed and I am not sure how to reach former colleagues. HR only confirms titles and dates. How do you ask politely?

Ask former colleagues and supervisors in a short message and give them a summary of the job you are applying for.

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