How long should I wait to text him, and what do I say?

I like a guy two years older than me, who I have only seen only 4 or so times in the last year very briefly, although every so many months we text TONS. It isn't a hardcore crush or anything, although Since I saw him a few weeks back at a friends party I'm thinking about him lots! I tried to Facebook message him, but he 'saw it' and didn't reply, which sucked because it took some courage to initiate it.

How long should I wait to text him, and at that point what can I say to hint I wanna hang out to see if this could lead somewhere, without sounding desperate in case the feelings are not mutual. And does the non replied fb message hint at anything?