Good (and common) question.
It's difficult advancing your startup / raising money without a CTO, but it's not impossible.
Here are first stages that you need to take:
1. Research your idea (how it will be done, costs) and the market [potential customers, competitors (what they're doing, how you're different) etc]
2. Refine your idea/business model/target market based on your research.
3. Share your idea with friends and get as much (negative*) feedback as possible (yes, I know that entrepreneurs are always scared that their idea will get stolen, in reality, this almost never happens).
* An important point for this stage is that you avoid the 'ugly baby' syndrome (if you show someone the ugliest baby in the world and say: "this is my baby, what do you think?" they will of course say that it's the cutest baby ever" because they don't want to offend you). So instead, say something like: "my friend has this idea he wants me to work on with him, I don't think it's such a great idea, what do you think?" - this way, they will feel more open to tell you the truth.
4. Refine your idea/business model/target market based on the feedback you received.
5. VALIDATE your idea (most important stage) - see how in my Clarity answer on this subject here: https://clarity.fm/questions/596/how-do-you-get-access-to-the-right-people-to-validate-an-idea

I've successfully helped over 300 entrepreneurs. I'd be happy to help you.
Good luck