Cyber bullies using apps like Snapchat, where evidence disappears

(CNN) – Tricia Norman thought she was being a conscientious mom, keeping tabs on her daughter's social media accounts.

But like many parents, she found monitoring online communications was getting harder with things constantly changing.

The growing trend of apps such as Snapchat and Ask.Fm, where messages easily disappear, have raised alarms; many are concerned they could be used to hide sexting or inappropriate posts.

And it's not just parents, they're a problem for law enforcement, too. Especially when something goes terribly wrong.

CNN's Sara Ganim reports.