Rouman Sanjuusou

Amana, Mizuho, and Riku are the members of the middle school 'romance' club, which has a rather vague mission statement. They decide to make it their club business to catch a recent serial pervert who exposes himself to little girls. Being cute young girls themselves, they may have an advantage over police in luring out the 'loli' pervert!

(Source: MangaHelpers)