Diabolo Vol 1

Diabolo Vol 1 by Kaoru Ohashi. A Horror manga rated Older Teen, published in English by Tokyopop in 2001.

A secret society lures teenagers into making pacts with the Devil in exchange for their wishes, and childhood friends Ren and Rai have already paid the price, gaining dark powers of their own. Those bound by such pacts risk losing their humanity as they near adulthood, so the two race against time to find Ren's missing cousin Mio and save other teens from the same fate. A dark supernatural horror series.