If you are looking to hire a developer who will become, eventually, your CTO and not just a programmer, then you are looking to hire a potential executive member who will represent your company. As such, it's important to look for someone who has the technical chops as well as the ability to be communicative with the outside world. What does this mean:
1) Do they have a github account (www.github.com)? If so, do they contribute to any public repositories? Do they file bugs? What does their communication on these repositories look like? Is it clear? Do they delegate tasks to other contributors in the repositories? If so, are they respectful and clear in their direction?
2) Any public interviews? Have they done any PR for the work they've done with other companies or for themselves? Are they able to convey technical concepts in easy to understand ways?
3) What's their social media profile look like? Yes, this matters for a CTO role. Do they have a twitter account? Are they considered an influencer in the tech circles they are involved in? Do they attend any meetups? Have they SPOKEN at any meetups?
4) What does their linkedin profile look like? Do they hop from one company to another? Are hey loyal? What does their testimonials say? Skip the testimonials that are vague and don't give you an idea of what the person did and what kind of impact they had. Look for testimonials such as: "A did B which gave us C and that made us D"
It's imperative that if you hire a lead programmer / CTO, you hire a leader and a representative. Otherwise, you're just hiring a code monkey with a title which will make it ever so harder to hire that leader once you find them.
Hope that helps!