"Twitter has a huge advantage over usual discussion boards: Twitts consist of
Short turns and
Long turns" (K. Borau, et al.).
Being a tweeter user for the first time during my studies I think that this is a good platform for expressing our thoughts without being criticized about our errors. Besides, following my peers and reading their tweets helps me once again go over the reading material. Each of us posts something different, thus we go over and over the lecture again.
Tweeter could be a good platform for some writing tasks for new learners as well, they would not be afraid to express themselves.
As described in the article "Microblogging for Language Learning: Using Twitter to Train
Communicative and Cultural Competence" by K. Borau et al. Twitter can be a useful tool to practice "
communicative competence". Learners can interact with each other, express their viewpoints.
In the case of developing speaking skills, Twitter and other social platforms can not be of much help, as some learners may be good in writing but bad in expressing their thoughts in oral communication.
Anyway, if the teacher sets a speaking task on Twitter, this can help the students to express their thoughts orally. This can be done through recording short monologues, or dialogues, role-plays.