This app was mentioned in 3 comments, with an average of 1.33 upvotes
As the guy before me has previously mentioned only apps that have Android Wear support will have an app on the watch. The best way to know is to look for the watch symbol on an app's description page.
Now as for Twitter there is an unofficial app for Android Wear called Looking for Twitter.
Edit: Mail for Android Wear is a nice version of Gmail for Android Wear. I also recommend to look at the other apps by that dev since they are also very good.
I use "Looking For Twitter" Edit : here is a link https://play.google.com/store/apps/details?id=com.droibit.looking
Looking is decent:
https://play.google.com/store/apps/details?id=com.droibit.looking&hl=en