Network with colleagues and friends. You may know someone who knows somebody who knows a professional writer capable of handling your project. Your acquaintance can connect you or perhaps arrange a meeting.
Do a Google or Yahoo search. When you search on keywords such as "ghostwriter," "book doctor" or "manuscript writer," ghostwriters and agencies that provide writing services will pop up. Try searching on variations of these terms, including "ghost writer" (separated into two words), "ghostwriting," and "book editor." Read through the websites carefully. Each writer has areas of expertise and specific strengths. For example, some ghostwriters focus on novels, others on general nonfiction, and still others are speech-writing specialists. For sites with specific information on this, see Resources below.
Post a free ad on the Internet. Many professional writers frequent specific sites in search of work. Consider posting your ad at Guru.com, Elance.com, Craigslist.com, and FreelanceWriting.com. At the majority of these and similar sites, it's free to post your job, and you're not under any obligation to hire anyone. If you don't find the right writer, just keep looking. Post a new ad at the same site, or try posting elsewhere.
Check with your local independent bookstore. The owner and manager are probably well connected to authors and members of the local writing community. Let the bookstore folks know that you're looking for a quality writer to help you with a book project. Chances are, they'll know someone who can help you.
Verify credentials. Once you've found a ghostwriter you'd like to work with, check her credentials carefully. Find out what experience this person has. Has she written any other books? Can she write in the tone and style you're looking for? Make sure to read several writing samples. Is the quality up to your standards?
Check references. Follow up by calling or emailing these people. Ask them what projects the writer did for them. Ask if they were pleased with the results. And ask if there was anything they didn't like about working with the ghostwriter. The more you ask beforehand about each candidate, the better decision you'll make.