If you're not making any money, you don't need to pay yourself. Once the company is making money, as the owner of a corporation in which you work, you need to pay yourself fair and reasonable wages for the job you are doing (to the extent the corporation can afford to do so). The government doesn't want owners actively working in small businesses claiming no salary and all income as profits, thereby dodging FICA, unemployment, and Medicare taxes. If you own a sandwich shop in which you do not work (you have a manager, a bookkeeper, etc.), you could legitimately take all profits as profits just as a shareholder in a large company does.
Anyone who isn't an owner has to be paid. Interns can avoid being paid only if you are using them through a program at their school and they are getting academic credit in some fashion. If that's the case, the school will make it clear to you and will typically have specific requirements you must meet--if only some kind of an agreement as to what things they will learn and a report back on their performance. If you're not being required to do anything, it's probably not a legitimate academic internship in the eyes of the government.
To be an independent contractor there is, as previously explained, a many-point test and in California it differs somewhat from the federal rules. Having passed a 2014 EDD audit with a clean slate approving our procedures and classifications, the clearest indication they are a true IC is that they have other clients and there is evidence they are running an ongoing business. A painter who works on your office is clearly an IC, although you may provide supplies and definitely direct the work and the timing of the work. While we direct a makeup artist on a shoot and provide the time and some direction in her work, they bring their own supplies, choose to accept the job or not, and have a lot of other clients, a website, etc. so it's acceptable to classify them as an employee. (Our shoots are 1-3 days, not a months of feature or TV filming, so the duration of the gig can override everything else in a review. In that case the makeup artist would need to be an employee, as it's not clear that they are actively running a true business at that point, but are instead rather working a series of temporary jobs.)
If someone is incorporated as an s-corp or c-corp they are clearly a business entity, not an individual, and it gets much easier. None of the tests are required because just the fact they are incorporated means you're not hiring an individual, you are hiring a company which is free to negotiate whatever terms it likes.
If you want a true co-founder either make them a corporate owner with you, or have them incorporate. It's not unusual for a business to have to do a little bit of free work as part of the pitch/proposal or to choose to do pro bono work because you believe in the cause or the relationship is valuable or perhaps for two small companies to team up on a big project--although in that case, I would expect their corporation would want part of your corporation or share ownership in the final work product.