Silent or secret partner

How can I find out who a secret or silent partner is for an existing LLC?

Check with the state to see if all investors must be included in the LLC’s articles of formation, or if all members must be a matter of record in an LLC.

If your state requires all investors/owners to be listed on articles of incorporation, just go to secretary of state website . Their should be a section to search for LLC/ corporation names, plug in the name to see the owners

How to find them? Sue them. It is often not required to be disclosed in public records.