I will tweet 7 times a link to your site or whatever message you want me to say on my accounts to 240000++ followers AND GROWING! I never every delete your promotion!
My main tweeter account has over 200,000 followers and is over 5 years old
Followers demographics=Mainly Adult and college students from USA, Canada , UK (85%) and 15% all over the world.
I can not guarantee or predict the number of hits, downloads, likes, etc. you will get - but if you're content is good, you will get the exposure you're looking for. If you have a good product, song or message you should get retweets.