to stalk someone on social media; to meticulously check someone’s posts (and their replies to someone else) on social media
It’s short for インターネットストーキング (internet stalking). Typically, people do this to obtain a large (and frightening at times) amount of knowledge about their “beloved” persons or someone they’re strongly interested in, such as their crush, exes (and their current partner), or the members of their favourite idol group. Most of them stalk casually and surreptitiously, paying as much attention as possible so that they won’t accidentally click the posts from ages ago. Others do this more enthusiastically and audaciously, liking every single post of theirs and sending them piles of direct messages.
I cannot resist stalking my crush on social media