Middle market companies seeking to build a sustainable business are facing what may become a new trend: young users leaving Facebook for other social networks.

In a high-tech world, reality can turn inside out and upside down quickly. Look at Facebook marketing. The service started among college students, expanded to high schoolers and older users, and then finally allowed advertising. The resulting rush to reach users of the social network propelled the company through enormous and continued growth.

For companies, Facebook seemed like a great way to reach next-generation customers who spend a lot of time online rather than reading newspapers and magazines, listening to the radio, or even watching television.

The question facing middle market companies is whether a Facebook marketing strategy is still a good idea. The answer is more complicated.

Understand Your Marketing Needs

To know whether a given medium is a good match for its marketing, a middle market company first needs to understand whom it is trying to reach and why.

Although many marketers seem to have a fetish when it comes to younger demographics, there are two basic reasons a company might want to reach a young audience: Either the audience is currently a natural match for its products and services, and the company wants to grow sales, or the company is cultivating future customers for a sustainable business.

So, why is a younger audience important to your company? Are they potentially buyers now? Are they the source of your future business, and is it realistic to develop a relationship with them or create a brand perception now? If so, you need to consider where to reach this audience. The viability of Facebook marketing now becomes a real question.

Is Facebook Still a Place for Youth?

Unfortunately, there is no easy or definitive answer. But marketing teams for mid-size businesses should take note of the following insights.

During Facebook's Q3 earnings conference call, CFO David Ebersman said that understanding youth engagement is difficult because "self-reported age data is unreliable for younger users." Instead, the company uses internal estimates that pegged usage among US teens to be stable from the previous quarter. Daily usage among younger teens did decline, but Ebersman didn't quantify the change.

Outside of Facebook, studies have produced conflicting results. According to anthropologist Daniel Miller of University College London, Facebook is "basically dead and buried" for teenagers. Rather than using it with one another, teens use the social network to keep in touch with older relatives. Teens are moving to Twitter, Snapchat, and Tumblr instead.

Pew Research Center noted that teens haven't abandoned Facebook, though their involvement with the platform "is complicated and may be evolving." Many teens disliked the increased presence of adults and "drama" of negative personal interactions. About 94 percent of teens had a Facebook profile as of last summer, and 81 percent said that Facebook is the social network they use most often. Just over a quarter had a profile on Twitter, and 11 percent had an Instagram profile.

Time for Testing

In other words, there is no tidy data that can tell you whether Facebook marketing will reach younger audiences - or even if it will be effective with older ones. In addition, a medium might work for some types of marketing but not others. The only certain answer is the one you can find through testing.

Facebook has some sophisticated audience segmentation available to advertisers. So, target some ads to your younger consumers and test the responses. Try promoted posts to see if they resonate with audiences. Does Facebook marketing work for your company in the youth - or any other - demographic? If not, is the problem with the social network or your advertising content?

Experimentation can determine whether you should continue to invest in a Facebook marketing strategy.

Erik Sherman is an NCMM contributor and author whose work has appeared in such publications as The Wall Street Journal, The New York Times Magazine, Newsweek, The Financial Times, Chief Executive, Inc., and Fortune. He also blogs for CBS MoneyWatch. Sherman has extensive experience in corporate communications consulting and is the author or co-author of 10 books. Follow him on Twitter.