The best place for an 11 year old to find a boyfriend is at school. To get a boyfriend, you should show speak to others, be nice to everyone, make friends and talk to the boy you like. Start out being friends and if he is interested in hanging out with you then you'll have a boyfriend.
The most likely place for an eleven year old to get a boyfriend is in a school or within the social network of the child. At eleven years old it is usually peer pressure that leads to worrying about boyfriends.
If you're 11 and want a boyfriend, you could write a note to the guy you like and ask if he'll be your boyfriend. If he doesn't say yes, don't feel too badly. There's plenty of time to find and experience love.