It's become very clear that teens are leaving Facebook in droves and that Facebook is feeling threatened. First, Facebook CFO David Ebersman reported a sharp decrease in teen daily usage on the world's largest social network. Then, teen sensation Justin Bieber announced he was investing more than $1 million in a new social network for teenagers, Shots of Me. Next, Facebook offered popular but pre-revenue teen mobile app Snapchat a whopping $3 billion cash--and it was turned down! This week Snapchat announced that 400 million photos are shared daily, significantly more than Facebook's 350 million daily photos.

Are teens leaving Facebook? Yes. Does the online behavior of teenagers often represent a technology trend worth looking at? Yes. So, where are they going? The answer to that is threefold:

1. New social networks. Clearly teens want to be on social networks where their parents aren't hanging out, and Facebook no longer fits that description. So they've flocked to Instagram (luckily for Facebook, which owns it), Vine (the video-sharing social network owned by Twitter), and perhaps soon, Bieber's Shots of Me.

2. Mobile photo-sharing apps. Especially outside of the U.S., teens are using What's App and Line to share photos and instant messages with each other and in small groups. These apps and others allow teens to be more private with their photos, videos and thoughts. (Again, mom's not watching!) 

3. Erasable media. Snapchat represents the growing trend of erasable media--ephemeral photos, videos and comments which are here one minute, gone the next. Perhaps the thought of everything you post on the internet living forever is too scary a thought for savvy teenagers to bear. Thought leader Erik Qualman wrote, "What happens in Vegas stays on YouTube, Twitter, and Facebook." But teenagers are realizing that it doesn't have to stay on Snapchat.

The question business owners are asking is. Does it really matter to your company?

That teenagers are leaving Facebook is an important, disturbing trend for Facebook and for its investors. (Disclosure: I'm an investor in Facebook.) But how much does it matter to you as an entrepreneur and to your business? The answer is simple:

If your target audience is teenagers, it matters a lot, and if your market isn't teenagers, it matters barely at all.

Daily usage on Facebook in the 34- to 45- and 45- to 54-year-old age demographics is up significantly year over year and quarter over quarter. Mom is still on Facebook. So if you're targeting mom, it may very well be better for you that Mom's kids aren't on Facebook--less waste for you and your marketing budget.

Entrepreneurs have a tendency to want to be on the cutting edge of technology--and there's nothing wrong with hanging out with all those teenagers on Vine, Snapchat, What's App, and Shots of Me. Just keep in mind that your No. 1 asset as an entrepreneur is your time. Do you want to spend your and your business's precious time hanging out with teenagers where it's cool, or hanging out where your customers are?