[z] Arista  Suggested by Dan Abnormal 
Twitteru  Suggested by rocamaco 
Pico Black  Suggested by MAWNS 
Social Logos  Suggested by Deleted user 605223 

Hey you can use Arista combined with pico if everything else fails. I did it in the past.

I think is this font.

I'm almost convinced that Social Logos is the right font if you just want the Twitter logo.