Please don't run a design contest. This destroys the creativity and will have a run down effect on the price. When you ask a designer to design a logo, prepare. Set out your ideas you want to achieve with your logo, define your identity and set out the principles a designer can work with. Then research online looking for a logo designer you like, brief them properly and work out a timeline, sketch ideas, concept design and final design.

Find designers on https://dribbble.com/ and see this post
http://www.creativebloq.com/graphic-design/pro-guide-logo-design-21221 on how to prepare in defining your identity/logo/style. #nospec m2c, good luck.