Officials say the search for South Carolina teenager Gabrielle Swainson is the largest and most intensive search conducted in Richland County in years. Swainson, 15, disappeared from her Richland County near Columbia home early Aug. 18 while her mother was at work, The State newspaper in Columbia reported. Now, more than 40 county and federal law agents are working on the case full time, including a behavioral scientist from the FBI\'s psychological unit at Quantico, Va., Sheriff Leon Lott said Sunday night. \"We are on this 24/7 and have a command post set up coordinating things,\" Lott said. Investigators said there were no signs of foul play, but added it was unlikely the teen left home of her own free will, as the only thing she took with her was her cellphone. Although law officers fear an abduction, Lott said, \"We remain hopeful that we will find Gabbiee alive.\"