I am 13 and I love to sing!
I practice everyday and people say I am really good but I want to be spotted and have a career in singing but how can I be spotted?

Look for local talent shows or send CDs of your singing to record companies. If there are any talent agents local to you, they would be able to help but you have to pay for their services.

How many open mic and show cases do you perform at each week ?

Youtube. With a good quality camera on a tripod or table, and good lighting. It has to look good as well as sound good. Keep it to 3 minutes, 4 tops, or people won't listen. Get everyone you know to view it and like it, to keep it going.
Go to auditions locally for any musical that needs a teen, even if you only sing in a chorus or have one line. Annie would be a good one with the main character your age. Find a theater group that might be willing to put that one on.

In other words, it's work.

I would suggest being very careful with Youtube. Once its on the Internet it's there forever ;)

Record a demo and send to as many places that work with artists of the genre you want to sing in. I've been trying for a few years now and have had no results so I'm not saying down your hopes but do not expect a yes from everyone. Play as many talent shows, open mics, etc as you can. Put up a few videos but like others have said keep it short and be careful. You want to show something different from you and every other person singing out there, maybe you play guitar or piano or where a hat or just something strange. Just make yourself more noticeable, stand out and don't be like everyone else. Be careful and I do wish you the best of luck. :)