This is a complex problem that I think many language educators can empathise with.
I guess it begins with trying to understand why students are not engaging in English. There are a number of factors that may have an impact, most likely different for different students.
It could be issues with the task (language level, meaningfulness), the environment (class atmosphere, peer relationships), student factors (anxiety, motivation, willingness to communication) or cultural (rules about speaking first, experiences speaking in a classroom setting).
For me, I make active participation in English speaking activities an explicit requirement of the course. Emphasis is placed on task completion and mutual understanding rather than perfect language (important for me teaching in Japan where concerns about being 'wrong' prevent many students from speaking).
I move around and jump into different conversations throughout a lesson, to become a native speaker interlocutor, but also to observe different students. Mixing student groups around regularly help students who are more or less motivated to meet. Teaching and practicing explicit communication skills is also important (circumlocution, turn-taking, etc.).
But at the end of the day, for me, students need to be encouraged to take responsibility for their own choices for how they use their class time.
Although recently, I was interested in why several male first year undergraduate students, at the back of a large class, were doing pushups during a speaking activity. Apparently those who spoke Japanese were being punished by the others in their group. An idea to contemplate..... :P
I do not believe that speaking in one's first language when engaging in ESL activities is detrimental. The important thing is to see whether the students are able to achieve the outcomes of an ESL activity in their second language English. In fact, Ofelia Garcia refers to the benefits of using one's first language to produce outcomes in one's second language in her discussion of 'translanguaging.' I believe that it is always better to let the students use all their linguistic and social skills in a language classroom. That may allow the students to bring various cultural insights in to the language classroom. For example, if you are in a Japanese second language classroom as a first language speaker of English from America, you may not want to brainstorm ideas for an essay on Thanksgiving with your American group members solely in Japanese, but you may produce the essay in Japanese. Learning to appreciate the beauty of an ESL classroom makes ESL teaching much more enjoyable!
Thank you for your comment. i agree with you about the factors affecting students speaking up which i will come through during the research. i also will not focus on using the language correctly; what concerns me is how encourage students to speak up in English
you are right L1 important for explanation and negotiation to understand the L2 but if we leave students as they want, they will not speak a word in L2 which makes it necessary to put some rules or strategies to let them using the target language mainly