Muslim ladies in social media

In the Name of Allah, the Most Gracious, the Most Merciful.

Assalāmu ῾alaykum wa Rahmatullāhi Wabarakātuhu

In the context, it is important to point out that Shariah has closed all doors leading to contamination of hearts and minds with any kind of  immorality.  We have our nafs which has a natural instinct of inclination towards evil. Furthermore, Shaitaan uses his power of waswasaa and incite our nafs to initiate evil. While making salam is an expression of courtesy and act of ibadah, Shariah considered the element of natural attraction to the opposite gender.  Shariah does not permit any form of immorality in the guise of practising Shariah or social courtesy.
Generally, the voice of a woman is soft and has an endearment in it. It could create attraction and excitement in a male.  It is precisely for this reason, Allah ordered women to avoid talking in alluring tone to strange men. Allah says: {فَلَا تَخْضَعْنَ بِالْقَوْلِ فَيَطْمَعَ الَّذِي فِي قَلْبِهِ مَرَضٌ وَقُلْنَ قَوْلًا مَعْرُوفًا} [الأحزاب: 32]  Translation: (Therefore) do not be too soft in your speech, lest someone having disease in his heart should develop fancies (about you); and do speak with appropriate words. (Ahzaab-32)
The above explanation will assist in making the following ruling easy to understand: 
It is permissible to hear a ghair mahram female voice in necessity only. 
A male should follow only males in social media classes.
It is advisable for a woman to avoid such classes in social media. 
Although, it is permissible for women to conduct classes attended only by women with full hijab including the covering of her face, while maintaining a straight and non-alluring voice throughout the sessions.

And Allah Ta’āla Knows Best.