Ah, righto. It is usually a good idea to state this up-front, in that case - experienced devs and designers see equity-only offers quite frequently, and sometimes the wording can accidentally make them sound like "work for free" requests.
If your equity-only offer doesn't generate any interest, the alternative is to self-fund so you can offer at least a cash mix. Designers will be happier to work at 50% rate than nothing, I expect! If the initial work can be done in a week, then the cash you'd need to inject would be relatively low, and would help demonstrate your own confidence in the project. You could also aim to get less experienced designers involved, to help them with their portfolio, but I would still aim to pay them something.