What do you think happens to you when you love, when you hate, when you feel rejected, appreciated, embraced, venerated, when you feel like you're being venerated without effort, you may feel like you're cheating and get a rise of it, or feel guilty from it, but in every case there's an endocrine response.
All of these chemical pathways are triggered by the hollow nonexistent social interactions, it can be an emotional rollercoaster and at the core is stimulation by endogenous compounds that can also be chemically addictive. You're finding a distinction that simply isn't there.
I dare you to show me any mention in the scientific literature of a physiological addiction to facebook comparable to opioid or alcohol dependency. A reductionist approach of "everything in a body is chemistry" does not mean all chemistry is alike. Normal emotions to not create the same long-term effects in body's neurochemistry as things like opioids do. That's why people take them - you can't really just get rid of an excruciating pain by thinking about something fun. You can by taking drugs, because drugs meddle with the body chemistry in a much stronger way than the normal endocrine response does. That meddling has a bad side - since it's so much stronger and invasive, it creates permanent damage. Looking at cats on facebook also causes chemical reactions, but not nearly as strong as the drugs do.
All of these chemical pathways are triggered by the hollow nonexistent social interactions, it can be an emotional rollercoaster and at the core is stimulation by endogenous compounds that can also be chemically addictive. You're finding a distinction that simply isn't there.