He can start by
sending this form to the employer.
The complaint form web page is
here.
See
here.
Also
Colorado Wage Act fact sheet.
Your friend is an absolute idiot if he's not a shareholder in this company. I can't think of any other reason someone would continue to render their services without being paid.
Additionally, the Wage and Labor dept can't order the payment of wages in excess of $7,500. By waiting so long, your friend has already capped what the dept can order the employer to pay, and may have to sue in court to recover his money.
If a company can't make payroll, then it's gone, insolvent, defunct. There won't be some magical turnaround.
Leaving the company
will not excuse the employer from payment of past due wages.
Also, I am not a lawyer but I am a CFO in FoCo, PM me if you want regarding this.