Search Results: no spark at a date

I'm a senior in HS and looking for a date to Prom, and I immediately thought of this guy (Junior, by the way) who I interact a lot with on social media & rarely in person. We seem to find a lot of the same things funny and have really similar views.
However, I did not want to be too forward with this guy and wanted to get to know him before I asked to go to prom (as friends). I decided to have one of our mutual friends set up a day for us three to all hang out together. So, on Friday a week ago we all hung out for a couple hours and we all had a lot of fun. This guy even made a point to go up to my younger brother and tell him how much fun it was to hang out with me because they are in an upcoming play together for my school.
So during the week after we hang out and I notice he seems to be making more eye contact with me and noticing me more (nothing that screams I LIKE YOU, but a little more flirty than usual). After school I finally decide to go up and talk to him right before he leaves. I sparked the conversation and he seemed pleasantly surprised, relaxed and smiled a lot. We had a very short conversation before he said he had to go and I ended with "I liked hanging out with you Friday", he said "Yeah, same" (or something of that nature).
A couple days and he seems to be acting the same towards me on social media. But yesterday I DM'd him on Twitter (I don't have his number) asking which nights he was in the upcoming play. Nothing else, and no smiley faces or anything flirty. He has yet to respond but I've seen him tweet things so I can be positive he has seen it.
Other things I know about him would be that based on his Twitter accounts (and he lets me follow his private twitter) he seems pretty insecure and I heard from his friend and ex-gf that he can be awkward around girls he does not know that well, however he seems confident in his friend group.
My question is, what is going on that would make him ignore a simple question? And what should I do?

I was set up on a blind date. It was a double date and the other two already knew each other. Anyway, the guy I was set up with I felt really comfortable with right alway. There were no awkward moments. Is it a good sign if I immediately felt comfortable with him? Does it mean he is good boyfriend material or does it mean there is no spark and we will end up being friends? I don't know, usually I get nervous around guys I like, but around him I feel different. Maybe this is good though? He makes me feel safe. Will he most likely end up being a good friend or something more?

The title pretty much says it all, just wondering others thoughts on this. If you go out with someone, how many times would you go out with them after the first date (if you felt no initial spark then) to see if romantic interest developed? Do you feel it takes time for the interest to grow, or do you think you will just know whether there is something 'there' or not by a certain number of dates, then cut it off if not? Please share your opinions!