For instance, you may install app lockers specifically meant for chat apps and social networking applications, namely the Chat App Lock and Messenger and Chat Lock. They would help in setting passcode for apps like Hangouts, Facebook, Gmail, Google+, and Gallery.
How to install app lockers on your Android device:
You need to open the Google Play store and find the Chat App lock. Select Install and accept the terms and conditions. Once the installation is complete, select the passcode that you wish to use for accessing the restricted apps. Enter the password of your choice and confirm the same. Then, you would be prompted to select a security question and answer. Once it is done, you would reach the Chat app lock main screen.
From this main screen, you would be able to protect various apps you wish to restrict access to. One may also prevent uninstalling and force stop from this same window. Another choice is to select a pattern to secure access instead of a password or pin.
In order to hide this icon, you need to select the Chat app lock icon and choose the option of enable hide lock icon from settings.
Similarly, one can install the Messenger and Chat Lock app and carry on from there.