Blackmail is a crime so forget it.
You need an accounting from your partners and if money has been diverted, try to get it back. You will be unable to do this without a lawyer.
Your whole business structure and the attention you are paying to the day to day operations is way below standard.
The above is general legal and business analysis. It is not "legal advice" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
In a Louisiana business (even if it's not incorporated), each partner has a responsibility (called a "fiduciary duty") to the business itself, which may or may not be the same thing as owing you money as an individual. Sometimes one partner will initiate a suit on behalf of the company to go after another partner for wrongdoing. Your liability with regard to the credit card company may or may not give you a personal right to go after him, but this really depends on more variables than we could go over in an online QA format.
Though it may not help in your current situation, for the benefit of those others reading, I recommend Nolo Publishing's "Craft Artist's Legal Guide" by Richard Stim to craft artist clients. It won't replace a lawyer, but it will help you understand your rights and potentially avoid situations like these in the future.
I'm a lawyer, but I'm not your lawyer unless we sign an agreement. While my practice involves a wide array of national and international issues, I am licensed only in Louisiana- where the legal system can be unique. The brief informational response provided here is not a substitute for legal advice, and you may need to act promptly to preserve your rights.
If you've lost trust in your partner you might be heading towards breaking up the business. If so make sure you consult with an attorney who can advise you before hand and guide you through the process of dissolving the partnership. I don't advise going the blackmail route.
This response is not intended to create an attorney client relationship and is based on the limited information available at the time of the response. Before acting on anything stated or referenced in this response you should consult with an attorney of your choosing and go over the specific details of your legal circumstances.