How do you find a designer for personal projects?

Find a designer that has already designed something. That's what I did for a webmail.

Ask him/her to use his/her work. behance & dribbble are full of skillful designers.

Ask around in your friends. My friends usually ask me to help them out.

Also you can post up in subreddits, facebook groups and forums.

Learn it yourself, it's a valuable skill.

Maybe try to post your project and ask for help on Designer News https://news.layervault.com/