Yes, try to contact your previous co-workers or Boss.
It is always best, to let them know, that you would like to put them down as references. So they have the head's up.
But many times, previous co-workers or a Boss, may not even be at that same job or company. So then, the company you are currently trying to apply to, will just call the HR department, to do a reference check. That is routine.
An application form, will have spaces in it for previous employment, to fill in. So, put down what your previous employment was. Even if that was years ago.
They need to know "work history" as a matter of routine, per the application form. And Professional References. ie: your previous Boss or Supervisor.
Even if you have not kept in touch with previous co-workers or a Boss, you still put down the company you worked for. And the name of your previous Supervisor or Boss. And if you do write down the names of your previous co-workers or Boss for "references", the company you are applying for, will do a reference check. And they will speak to the HR department. Even if, those previous co-workers or Boss, is no longer at that company.
"Reference checks", are done to confirm your employment and job title, at previous jobs. They CANNOT, ask subjective questions or about if you were liked or not. That is against the law and HR policies. They will only, confirm or not if you were employed there, if you are considered re-hireable or not, and your position title and the dates of your Employment.
"Personal references" would be only that. Personal references. Not job related references. And it would not confirm your employment at a previous job.
I used to work in HR.