Just when you finally got on Facebook, rediscovered childhood friends and changed your avatar to a red equals sign, the teenagers have moved on to something else.

Now what?

If anyone might know which apps and sites teens are using that parents should get familiar with, it's Adam McClane, a former youth pastor, blogger and author ("A Parent's Guide to Understanding Social Media," which he co-authored with Mark Oestreicher) from San Diego.

Two that come to mind, McClane says, are Snapchat, a photo message sharing app that allows users to post messages, photos and videos to a controlled list of recipients and set the amount of time the posts are visible. The other is Twitter, but not the way we have been using it.

Snapchat, he says, which targets 13- to 19-year-old girls, is "bait. It's built on a lie." It promises that everything goes away. It doesn't, McClane says. That's not the way the Internet works.

The company says it doesn't store images, but images are stored — they have to be, in case a law is broken and evidence must be produced. Also, what's to stop another "friend" from grabbing a screen shot of something you've posted?

So while 90 percent of teens are using this app innocently, be aware that anything posted could resurface.

Instead, he encourages students to use Instagram, which is built on openness.

"It's more transparent," McClane said. "There's not an assumption that everything is private. When you tell adolescents something is private, that's when the bad stuff starts to happen."

Meanwhile, as you've been tweeting a photo of your Caesar salad to anyone who follows you, your teen has created a number of private accounts in his or her name for different groups of friends. All accounts are closed, so you must seek permission to be a follower. So basically, they have private texting circles.

Statistically, McClane says these three — Snapchat, Instagram and Twitter — are the three parents should know.

Here are some other tips:

Talk: "Your kids really do want to engage with you about their online behavior," McClane says. "I would encourage parents to create an Instagram account. Try it out. Post your food. Ask them how something works."

Explain: With social media, you're not the consumer, you're the product, he says. Companies collect data so they can send it to marketers. Remind kids: "Everything I ever do online is stored so someone can sell it."

Privacy? Yeah, right. There is no such thing as Internet privacy, only perceived privacy, McClane says.

In the database world, it all goes to the same place. Even when you delete something, it doesn't go away, you just can't see it anymore. Help them understand how the Internet works.