This has also been a real challenge for me when I started using Social Media accounts, and I believe it is for everyone.
However, I've come across 2 useful web services that hopefully may help: Twiends & Social Clump. Both of them are used in growing your number of Twitter followers, Youtube subscribers & viewers, & Facebook page likes.
Please see the separate thread that I'll be starting with a comparative analysis for both these sites.
These are quite new services (especially Social Clump) that look promising, and I'd be glad to share my experience with them to everyone.