Real content does not coincide with the form. Most people judge after the form, barely on the content. Few would apply if a woman confesses the truth: “I'm standing here with four kids, my husband has left me, my dad has expelled me, the street is no longer feeds me because I am getting older. No one needs me either in Dubai, send me money to charge my phone so that I have at least my daily dose of drugs.” Or in case of men: “I made a bet with Joe and other guys that I can collect here four girls today. It's going to be a party, Joe brings the material, my business are the women.” I don't think I'm far from the truth. Who does in this world need deep thoughts? And the TV, the media are just putting a surplus to this emptiness! It's getting a good business! Yes, it is, but we are losing what makes us human!
There are cultures, social norms and those are constantly changing. We scold America, even though beside the existing superficial phenomenon there is formed a sort of convention in business life, or above a social level, morality and setting of boundaries has begun to show a value. However, in the most rigorous Islamic world, contrary standards are spreading. They believe to be in line with the world trend if their conduct converts towards the Western, free-moral style. Hungary is what it is. Instead of standards, instinct-based survival is the trend.
“An old homeless, financially in minus who lives from day to day, with several children is looking for partner. What he has: debt, speech, and part from the ancient knowledge that makes him able to quote from the Quran and classic literature. He is looking for a partner who visits him once a week, makes cleaning, doesn't talk, doesn't import her own troubles, but puts twenty thousand forints on the bedside table and leaves in the morning silently.” Would be there any candidate for this? Never! Maybe the knowledge of the old man, if not the survival, but would serve a better comprehension of life and worth more than the cheating-guys standing with fake cars. But this was just an example, don't take that as a personal advertising. My goal is to show: the content and the need searching for it is extinct from us. Today, this is the case here, in other places different. We should never consider a condition as permanent. Norms and traditions are in constant change. Just one important thing: does the value remain constant in the change? Many places the value remains but in many places it disappears. Therefore, I warn anyone to attach too much importance to the surface! In vain there is a Rolls-Royce or a hijab in the picture, if in reality it doesn't couple with value.
Once upon a time dating had rules. Elderly members of families were looking for youths who were matching. It is true that over time this has been overwritten by interests, forced marriages, etc., as in human hands everything changes the original direction. But if we are already relying on ourselves, go to a silent place and think it over without emotions, instincts, and hormones: where an emotionbased relationship leads to if we are going to be build our future on it? What is the probability that couples will find each other on social network sites? I'm not saying it is impossible, but what is the probability?
We tend to use benchmarks that have lost their credit. We believe that the Academy of Science is the benchmark for science, though it may be that this science serves only the goals of a narrow group.
We follow the Sunnah, traditions where the written form is excellent, but the man to whom it was once tailored has worn off. Not only man but also age has changed. It was once the trend:

Narrated Ma'qil ibn Yasar:
A man came to the Prophet (peace be upon him) and said: I have found a woman of rank and beauty, but she does not give birth to children. Should I marry her? He said: No. He came again to him, but he prohibited him. He came to him third time, and he (the Prophet) said: Marry women who are loving and very prolific, for I shall outnumber the peoples by you.

Book: Marriage (Kitab Al-Nikah) Grade
: Hasan Sahih (Al-Albani)
Reference: Sunan Abi Dawud 2050
In-book reference: Book 12, Hadith 5
English translation: Book 11, Hadith 2045

The above hadith is true when there is a man who takes care of his family, supplies his children with knowledge in order that they become more than he is. And there is a woman who can provide an emotional foundation for her husband and children, in her priority the cause of her family is before the beautician or fashion. Hadith is about building a quality society, not about fucking and producing waste on mass level. Huge difference!
Thus, there is no specific answer to the question whether advert of marriage, dating on a social site is permissible according to Islam or not? If there were sincere human revelations, manifestations of real intentions that please God, then why would it be Haram? But there are not any! Most people here are lying! Therefore, the question falls back to its originator. The relationship what you enter to, qualifies you. The real question is, can you reckon this relationship with Allah? Not before your family, your society, but before Allah! This is the question and there is no general answer. Every case is different.