Most important.

1. Have you and your friend talked casually about prom night plans? (+25 points)

2. Has your friend asked you if you already have someone to go as to prom with? (+20 points)

1. He connects with your electronically (Texting, IM, Facebook, Twitter, Emails) with you at least once a week. (+15 points)
2. He tags photos of you on facebook, he tweets his most personal thoughts at you. (+15 points)
3. You spend time with him during the weekend at least twice in the last month. (+10 points)
4. You think his buddies are cool, your friends think he is hot. (+10 points) 
5. When you hang out together you always have fun things to say to eachother. (+10 points)
6. He responds quickly to all of your texts (well most, I suppose sometimes he isn't around his phone) of the time. (+5 points)
7. Your cell number is saved on his cell. (+5 points)
8. He doesn't have a prom date. (+5 points)

1. Friends say he is thinking of asking someone else. (-20 points)
2. When your with friends, he doesn't find reasons to talk to you one-on-one. (-15 points)
3. You never hang out alone, you only see him when you are in a group. (-15 points)
4. You don't hang out at school. (-10 points)
5. He flirts with everyone not just you. (-5 points)

Score

Yes, do it!  You are good friends now, you might be more later, but either way he probably wants you to ask him to prom.  

Now its more iffy.  He might be a good prom date, but he might not be a good choice.  If you aren't sure find a reason to be alone with him outside a group and see if you have a fun time.  If all is well then you can ask him.  But make sure he hasn't asked someone else.

Look for someone else.  You are members of the same group not truly compatible friends.  You make think he is cute, you may think he is hot, but he'd probably have more fun with his friends than with you at the prom.