If by "encourage" curl, you mean hold the curl in place then the answer for styling products is "yes." If you mean "create curly hair from straight hair" the answer is sadly no.
If you have naturally curly or wavy hair Quidad has shampoos conditioners and styling aids that encourage maximum curl and minimize frizz. I didn't think these would work until I tried them pretty amazing results, at least on my hair. (http://www.ouidad.com/?sc=ppc_GT2_OUITTR_MSP)