Facebook Page Plugin doen’t responsive because It is frame that embed from facebook page profile.
making it responsive by adding style on frame width:100%.

The solution

you can put code in your css as below:

.fb-page span,
.fb-page span iframe[style] {
width: 100% !important;

The end results.

for my website,I have tested with above code in css and Finally It work well.
I hope your work will be fine.