Asking students for instant fluency in a second language is doomed to failure. Give your students ample time to practice what they are going to say and give them small–bite sized chunks of language at first. When their confidence grows you can allow them more free practice time. Try this activity below.
Animal Dictation
Dictate an incomplete sentence to the class: My favourite animal is...............
Ask the students to complete the sentence. Then ask the class the question: What's your favourite animal? Choose a quiet student and ask them to read their sentence out to the class.
In general it may be a good idea to let students write down what they are going to say first. It doesn't demand risk taking, it builds confidence and psychologically they are more likely to respond to further questioning from the teacher or other students.