Check whether the person’s name appears on the list or not. If not, it is more likely the user is not using Line anymore. It is a quick and fast way to tell if someone is in Line.
Method 2: Checking Recent Posts

If the person is online, then it’s more likely that the person will be sharing posts in Line. You will have to navigate to the person profile that you wanna check. Then click on the post option below on the screen and check their recent posts. You can check the dates of the posts if you see an upload time ad date recently then you can determine that the person is online probably.
Moreover, you can also check for the comments on the recent posts of the user to determine whether if he/she is online. If you notice increasing comments and reply, then you would know the person is online.
Method 3: Checking Profile Online Batch

The last option you have, to determine whether if someone is online in Line is to check their online batch. So, just open up the person profile that you want to check for, check his/her Status message. You will see a green batch over there. If not, that means the person is offline.
Conclusion
There are other social media apps that show the online status with a green dot or simply by letters. However, if you are using Line, you are not that lucky one to keep track of other weather if they are online or not.
There are no indications like green dots, blue tick, etc. to label a person online in Line. You can only try a few tricks to determine if the person is online. The fastest way to know if someone is online is by sending them a message. If they saw the message or respond to it, you will know the status of the person.
The other way to determine if someone is online or not is to check their profile status message, whether it changes due to time or not. Moreover, you can check for the recent posts of the person to know if he/she s online. Also, you can check their comments on their posts for more clarity.