This article will guide you on how to see which of your friends are currently active on Facebook Messenger.
Steps
Using a Phone or Tablet

Launch the Facebook Messenger app. The app features a blue chat bubble icon with a white lightning bolt inside, typically found on your home screen or app drawer (Android). If you're not logged in, follow the on-screen instructions to sign in.

Tap on the contacts icon. This icon resembles a bulleted list located at the bottom right of the screen, next to the large blue circle.

Press the
Active button near the top of the screen. This will display a list of all contacts currently active on Messenger. A small green dot will appear next to the profile picture of active friends.
Using a Computer

Visit https://www.messenger.com from your browser. This is the main page for the Facebook Messenger app.

Log into your Facebook account. If already logged in, you will see a list of recent conversations on Messenger. Otherwise, click Continue as (your name) or enter your login credentials as prompted.

Click on the blue gear icon located at the top-left corner of the screen.

Select the Active Contacts option. This will display a list of contacts currently active on Messenger. If only your name appears, toggle the switch next to it to On (green), and the active contacts will be shown.