I think, more importantly than hiring a realtor, find an experience property manager or tenant placement expert in your area. Sure most of the time, this qualified individual will be a realtor as well. But the idea is to find someone who specializes in leasing. These days, I have found so many agents who are in the rental market just because it's HOT and they do not have the marketing experience needed to handle rentals.
So look for a property manager or an agent who has experience in rentals. In the meantime, do some marketing of your own to begin lining up prospects (then allow a pro, when you find one, to take over and screen those tenants if you DO get some inquiries). You can use free websites to post your listing. Craigslist.org, kijiji.com, backpage.com, and for a fee you can list on rentals.com
Again, all these sites may get you some hits and tenant inquiries, but I 110% recommend you allow a management company to handle further advertising, scrfeening/qualifying, etc for your properties potential tenants. You will be looking at anywhere from about 70%-105% of one months rent for tenant placement. And 10% of monthly rent is pretty standard for monthly management services.
Best of luck,