While a long and never-ending project, developing and maintaining a mailing list is necessary for staying in contact with people who can hire you. Here's a list of resources:
1. Friends and family - Let them know what you're doing. If they don't have jobs for you, through six degrees of separation they will help sell you to their friends.
2. Internet - Search for advertising agencies and production companies in your city and beyond. Simply type in "production companies" or "advertising agencies." Lots of listings will appear. You can also look in the online yellow pages. When culling through lists, do your research. Not all of them will be appropriate for your services and talents. Go to that company's website and determine if it is a good fit. Try to find who handles voice talent submissions. Large advertising agencies do the majority of their casting through talent agents, so they're a tough sell. Small-to medium-size businesses are better at accepting cold calls.
3. Resource Guides - Several websites around the country offer resource information and casting notices.
Voiceoverresourceguide.com in Los Angeles and New York, Reel Directory
in San Francisco, and producershandydandy.com in Washington, D.C., are just a few of them.
4. Talent Agency lists - If you have agency representation, ask your talent agent if you may use their contact list for a targeted promotion. Many of them will not allow it, but some will if they feel it's a team effort and they approve your materials. Don't expect their list to go out of the office, though. It's proprietary information. If you get responses back, then you can start your own list.
5. Social Networks - Yes, you can get work through listings in LinkedIn and Facebook. You're connecting with friends and friends of friends. It's just another approach to the old-fashioned face-to-face time. If you set up groups, remember to be a problem-solver and not a problem.
Whatever promotional ideas you choose, keep them unique and original. Old, rehashed ideas have little or no impact and inspire.