How are you seeing someone, even casually, if you can't just pick up your phone and text them? How did you meet? Have you been on a date? Have you spoken about meeting again? Has he messaged you? Do you want a casual relationship or do you just mean you've started dating and it hasn't developed yet but that's what you're looking for - committed not casual?
I'd just text "hey, what are you up to today? I'm <whatever you're doing>"
Just say anything to get the ball rolling.
What would you send to a friend today?
"4 more sleeps!" "Work busy today, be glad when Xmas rush is over"