Hah, I've had similar issues, but my participation level for speaking activities really varies by class.

At least for pair work, I've had success with printing the dialogues and assigning partners.  If you let them choose, often the shy or unpopular students won't want to pair up and will just sit there quietly.  I also tend to require some sort of production.  Often this entails students filling in blanks on a dialogue together, practicing it together, and then practicing it for either me or the class as a whole when I stop by their desk or call them to the front of the room.  The knowledge that they will have to have some sort of response ready seems somewhat motivating.

I have had issues in the past with certain students not wanting to work together, but I find that generally they vastly prefer working in pairs to working alone. Maybe a couple times making them work alone will get them keener to work in pairs? I also assign group work fairly often (typically four people max). I find that sometimes the ones who hate to work together I really have to hover around. I've also lately been making the students who don't finish their worksheets go sit in the corner to finish them while the rest of us move on to whatever activity I am doing to end the lesson. Or in the case when there is no activity, they have to stay after the bell. Amazing how easy it suddenly becomes for them after that!