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.

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

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.