Jeremy Herve on "[Plugin: Jetpack by WordPress.com] Jetpack facbook like box width issue"

You should be able to change the box's width, up to a a width of 400px, as defined by Jetpack. If you want your Like Box to be wider, you'll have to build your own Like box, following the instructions int he Like Box page:
https://developers.facebook.com/docs/reference/plugins/like-box/

I took note of your feedback though, and created a trac ticket about this issue:
http://plugins.trac.wordpress.org/ticket/1811

We'll see if we can increase the maximum width in a future Jetpack update.

Thanks!