Here are a bunch of databases of Missing Children/Persons:

Popular Databases:
http://www.missingkids.com/	Missing Children | MissingKids.com
http://www.pollyklaas.org/missing/index.htm	Missing Children | Poly Klaas Foundation
http://www.amw.com/missing_persons/browse-by-last-name.cfm	Missing Persons | America's Most Wanted
http://www.interpol.int/Missing-Persons	Missing Persons | Interpol
http://www.namus.gov/	Missing Persons | NamUs
http://www.ncis.navy.mil/ContactUs/Pages/MissingPersons.aspx	Missing Persons | US Navy & Marines

State Databases:
https://app.alea.gov/Community/wfSearch.aspx?Type=15&Status=5	Alabama
http://www.dps.state.ak.us/ast/abi/bulletin.aspx	Alaska
http://www.maricopamissing.com/	Arizona
http://www.facebook.com/pages/Phoenix-Police-Department-Missing-Unidentified-Persons-Page/158284437538528	Arizona | Phoenix
http://www.acic.org/missing/search.php	Arkansas
http://dojapp.doj.ca.gov/missing/default.asp	California
https://www.colorado.gov/apps/coldcase/search.html	Colorado
https://www.findthemissing.org/en	Connecticut
https://www.findthemissing.org/en	Delaware
http://mpdc.dc.gov/unsolved	District of Columbia
http://pas.fdle.state.fl.us/pas/person/displayMissingPersonsSearch.a	Florida
http://www.sheriff.org/apps/missingpersons/	Florida | Broward County
http://gbi.georgia.gov/cases/missing-persons	Georgia
https://www.findthemissing.org/en	Hawaii
http://ag.hawaii.gov/cpja/mcch/hawaiis-missing-children/	Hawaii Missing Children
http://www.co.maui.hi.us/index.asp?NID=425	Hawaii | Maui County
http://isp.idaho.gov/BCI/missing/	Idaho
http://www.isp.state.il.us/crime/missing.cfm	Illinois
https://portal.chicagopolice.org/portal/page/portal/ClearPath/Communities/Missing%20Persons%20Alerts	Illinois
http://www.in.gov/isp/2333.htm/	Indiana | Chicago
https://www.findthemissing.org/en	Kansas
https://www.findthemissing.org/en	Kentucky
http://identifyla.lsu.edu/	Louisiana
http://www.maine.gov/dps/msp/criminal_investigation/missing_persons.shtml	Maine
http://www.marylandmissing.com/home.html	Maryland
http://www.michigan.gov/msp/0,4643,7-123-1589_31786_32000---,00.html	Michigan Children
http://www.mfia.state.mi.us/awol/	Michigan Adults
https://dps.mn.gov/divisions/bca/bca-divisions/administrative/Pages/missing-unidentified-persons.aspx	Minnesota
https://www.findthemissing.org/en	Missing
https://www.findthemissing.org/en	Missing
http://www.mmup.info/	Mississippi
http://www.mshp.dps.mo.gov/CJ51/map.jsp	Missouri
http://www.kcmo.org/police/FAU/index.htm	Missouri | Kansas City
https://doj.mt.gov/missing-persons/	Montana
https://statepatrol.nebraska.gov/MissingPersons/	Nebraska
https://www.findthemissing.org/en	Nevada
http://www.washoesheriff.com/sub.php?page=missing-persons	Nevada | Washoe County
http://www.nh.gov/safety/divisions/nhsp/missingpersons/index.html	New Hampshire
https://www16.state.nj.us/NJSP_Amber/MissingPersonList.jsp	New Jersey
http://missingpersons.osogrande.com/	New Mexico
http://www.criminaljustice.ny.gov/missing/index.htm	New York
http://www.nyc.gov/html/nypd/html/missing_persons/missing_persons.shtml	New York City
http://www.ncmissingpersons.org/missing-persons/missing-north-carolina/	North Carolina
http://www.ag.nd.gov/BCI/ColdCase/coldcase.html	North Dakota
http://www.ohioattorneygeneral.gov/Law-Enforcement/Local-Law-Enforcement/Ohio-Missing-Persons/All-Missing-Persons	Ohio
https://www.findthemissing.org/en	Oklahoma
http://www.pamissing.com/missingpersons.html	Pennsylvania
https://www.findthemissing.org/en	Rhode Island
https://www.findthemissing.org/en	South Carolina
https://www.findthemissing.org/en	Tennessee
http://www.tbi.state.tn.us/missing_children/miss_child.shtml	Tennessee Missing Children
http://www.txdps.state.tx.us/mpch/	Texas
http://publicsafety.utah.gov/bci/UTAHmissingpersons.html	Utah
http://www.vsp.state.va.us/MissingPersons.shtm	Virginia
http://www.vsp.state.va.us/MissingChildren.shtm	Virginia Missing Children
http://www.wsp.wa.gov/crime/misadult.php	Washington
http://www.wsp.wa.gov/crime/mischild.php	Washington Missing Children
http://www.wvsp.gov/missing-persons/Pages/default.aspx	West Virgina
http://www.missingpersons.doj.wi.gov/missingkids/index.asp	Wisconsin
http://www.missingpersons.doj.wi.gov/missingkids/unidentified/index.asp	Wisconsin Unidentified