I found this article on the FBI website. I only copied a bit of it - the article has more information.
Child Abductions
Known Relationships Are the Greater Danger
A majority (68 percent) of the child abduction cases the FBIs Child Abduction Rapid Deployment (CARD) team has assisted in has resulted in the identification of an offender who had a relationship with the child victim.3 Moreover, an RSO was involved in only 10 percent of the investigations, 5 percent of who knew the victim.
In FY 2009, 63 percent of child abduction cases involved an offender known to the victim; only 1 percent were RSOs.4 In FY 2010, 70 percent of child abduction cases resulted in the identification of an offender who had a known relationship with the victim; less than 1 percent of the abductors were RSOs.5
http://www.fbi.gov/stats-services/publications/law-enforcement-bulletin/august-2011/crimes-against-children-spotlight