Ok well I met this girl like 3 weeks ago and I have been talking to her almost everyday via text. We kissed one night and the next day I asked her out and she said she will think about it. And since then we keep texting but she hasn't given me an answer...

Should I keep texting her?
Or
Stop texting her and see if she keeps trying to text me?

I think you might need to be a little more clear.

Text her with an actual date. Where you want to go, what you want to do.

To leave it up in the air like that, she's probably wondering what you have in mind, and when you're going to ask.

Why don't you call her to ask her out instead?

Be more direct and you will get a more direct answer.

If she still says that she "will let you know," then chances are she's not really interested in dating and is happy texting you only.

Try asking her out again but do it in person. In person is always more direct. Continue texting.

Well, she isn't playing "hard to get" necessarilly. Not all girls, or guys, relate kissing to a relationship.
That could have been just a "transition" between friends, and deciding on something more. Keep trying, but ultimately you will have to wait.

Maybe she just wants time to get to know you better or she may be really busy.
Do you ever see her or spend any time with her that you could ask her in person?

Ok modded... ask her out on a date. Have the time, the place, and the activities all ready to go. Girls like a guy who can plan, and make decisions on their own/take initiative. If she denies you, or says "I'll think about it", then cut off all communication with her until she makes the effort to SEE you.

Dating is not suppose to be a game, even though many play it like it is... I'm all about being direct, and as the saying goes "Sh!t or get off the pot"... If she likes you she will go out with you and see where it goes. Endless txt messages with no face-to-face time sounds like a very boring start to a go no-where relationship...

Thumper

Forget about her!

All that texting and your not getting any where? Ask her in person for a date and see what she says. Sounds like she likes you as a text buddy but not for romance. You better find out before you get any more involved than what you are.