The PS2, X-Box and PC versions, all have different ways to recruit gang members, as you'd expect, so I'll list all three here so It's easy to understand for everyone.
Playstation 2 Version
To recruit fellow gang members on the Playstation 2 version of San Andreas, you need to click and hold the R1 button (



X-Box Version
As with the Playstation 2 version, It's quite the same to recruit with the X-Box version. In the same manner, lock onto the prefered gang member, and press the up button on the D-Pad, just like the PS2. As with the PS2 version, simply hold the up button on the D-Pad to un-recruit the member. Also, pressing up will call the gang members to you, and pressing down will make them stay put.
PC Version
The PC version would probably be the most simple way of recruiting in the San Andreas world, and to do so, all you need to do, is aim your mouse crosshairs at one of your green grove street gangsters, press the right mouse button and press the "G" or "H" button on your keyboard. There you go, you've got your own gang to go around with you and help you finish missions, etc.
Please note: The controls may be different if you have changed the buttons around. As with the other two versions, hold "G" to un-recruit them.b
Hopefully this will slow the amount of threads about the recruiting aspect of the game.