Freelancer and Upwork (formerly oDesk) are freelancing sites that facilitate and streamline the process of hiring virtual (or remote workers).
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Each of these sites have their own approach, but in essence, all of these companies allow you to do more or less the same thing.
You can post a job description, have people bid on the work, negotiate on price, and look at previous ratings and work history before settling on either a contract rate, or a pay-per hour agreement.
Generally, money is escrowed (or held) by each of the websites and they release the payment to the worker when the work is complete (skimming a neat profit at the same time – typically 10-15% of money that changes hands).