I'm interested to hear what people have to say, however whenever I receive the "I miss you" text from a HB I always reply with "I kinda sorta miss you too". I like using this because it leaves a little doubt for her to dwell on, makes her think.
You could initiate it with a "I kinda sorta miss you" text.
If she questions "kinda sorta?" then I'll usually reply "yeah, things have just been so crazy lately," (you can supplement this with: how busy you are, that your friends want to go out all the time, etc). "but I had a moment to think of you

"
Or is you want a cocky funny "I'd miss you more but I'm beginning to forget what you look like

" this will occassionally get you a pic message, which is always pleasant.
Saroza