It's very hard to make your students speak in English especially teenagers. They're afraid of being bullied by their peers but games, warmers or fillers have a magic effect on teenagers. while they're playing or doing the activities they don't think that they're speaking or writing in English.
Here is an activity that I've learned from a workshop that I attended and I use in my classes. It can be used as a warmer, filler or you can extend it to a writing activity.
TANGO SEATED CHAIRS
This will be a pair work activity so students find their partners and sit opposite to eachother as they're doing tango. One of the students can see the board but the other can't.The student who can't see the board has to have a pencil and a sheet with him/her.
I draw a picture on the board, the student who can see the board has to describe it to his/her friend and the other has to draw it.
To prevent the describing partner to use his/her hand I ask them to sit on their hands.
The picture can be anything you can draw no artistic talent needed.For example I draw a beautiful shore with the sun above with full of trees and people sunbathing.
To extend the activity I ask the pairs to note down ten adjectives that this picture reminds them. As a follow up activity students can write a poem using these adjectives.