I'd suggest technology is a key attraction. People involved in startups are there not only because it might get big, but also because the technology they are using excites them.

Hiring (and retention) is currently so difficult that the ability to do it well is one of the major factors separating the best founders/startups from the rest of the pack. Ideally you're extremely charismatic, resourceful, and well-connected, and your company is attractive, interesting, and promising.

Jedi mind tricks.

Increase their ownership of the company. You're asking them for investment.