Since you know that the company is not turning a large enough profit to make raises a viable option for the employees, I would say you should not approach the owners about this.

If it was agreeable and you did receive your raise, there is the possibility of other employees in the office catching wind of this and demanding raises of their own.

The owners are aware that you know and understand the situation and may even feel hurt that you asked the question of a raise.

It might be a better idea if you quietly scan the field and search your other options of different positions within the industry.

It may, however, be possible to discuss the situation with the owners and submit a proposal for sharing in the profits instead of your salary. Since you were one of the start up employees, the owners may be apt to receive this scenario better.

You would need to do a lot of work and taking stock of your savings, if you are able to forgo your paycheck in lieu of a share of the profits. In the long run you may just lose out with this plan. If the company is headed in a positive direction, you may come ahead.