( CNN ) -- Investigators continued their search Tuesday for a 7-year-old girl who was reported missing after her mother was found dead in Oklahoma . `` We 've got to find that little girl , '' Special Agent Ray Homer of the Oklahoma State Bureau of Investigation said . `` We 're doing what we can . '' The girl -- Aja Daniell Johnson -- was reported missing from Geronimo , Oklahoma , late Sunday , the bureau said . Her 37-year-old mother , Tonya Hobbs , was found dead inside a parked RV . They also are trying to find the dead woman 's estranged husband , Lester William Hobbs , 46 , the bureau has said . Lester Hobbs and Aja are presumed to be in Hobbs ' car -- a white 1992 Toyota Paseo with Oklahoma tag No . 577-BPW , police said . Police were looking for Hobbs and Aja in Oklahoma and Texas . Authorities were working with the National Center for Missing and Exploited Children on Tuesday to set up a toll-free phone line and put Aja 's photo on a Web site of missing children , Homer said . They have had no communication with Lester Hobbs or anyone else that would indicate Aja 's location , he said . Tonya Hobbs and her daughter visited Lester Hobbs at his sister 's home , the bureau said . Lester Hobbs is not Aja 's biological father , police said . Texas authorities also issued an Amber Alert , Texas Department of Public Safety spokeswoman Lisa Block said . Authorities believe Hobbs has connections to Rockport , Texas , and the alert was issued preemptively , she said . Tonya Hobbs and her daughter were last seen Saturday night . Authorities did not say how Hobbs died , but the bureau said investigators believe someone killed her . The RV belonged to Lester Hobbs and was parked at his relatives ' home , Richard Goss , agent in charge of the bureau 's Lawton , Oklahoma , office , told reporters . Hobbs ' relatives became suspicious Sunday after they did not see Tonya Hobbs or Aja . One of them pried open the RV door and discovered Tonya Hobbs ' body , he said . Lester Hobbs and Aja were gone , Goss said . The Hobbses were separated , but apparently Tonya Hobbs was visiting Lester Hobbs in an attempt to reconcile , Goss said . The couple had been together for about five years . The Comanche County , Oklahoma , Sheriff 's Office said Aja has a medical condition that requires medication . `` Our main concern at this time is to find the little girl , '' Comanche County Sheriff Kenny Stradley told reporters . `` We know that she does need some medication , '' and authorities were checking leads regarding that , he said . He did not specify Aja 's medical condition . Goss said Lester Hobbs has an extensive criminal history , but did not elaborate . The sheriff 's office said he had prior felony convictions . Lester Hobbs was supposed to appear in court in Lincoln County , Oklahoma , on a DUI charge , Goss said , and did not appear , so a warrant has been issued for him . Aja 's biological father was awarded emergency custody of her in November , according to Oklahoma County District Court documents obtained by CNN affiliate KWTV of Oklahoma City . At a hearing , Tonya Hobbs -- identified as Tonya Dunkin in the documents -- and the girl 's father , John Johnson , agreed that she would have supervised visitation with Aja and keep the girl away from Lester Hobbs , the documents said . Aja is 4 feet tall and weighs 59 pounds , Goss said . She has brown eyes , and her hair is brown with the ends dyed black . Lester Hobbs is about 6-foot-1 and 190 pounds , with hazel eyes and brown hair , according to the Oklahoma State Bureau of Investigation . The agency released a picture of him and said he has a mustache but no longer has a goatee . Geronimo is about 12 miles south of Lawton , Oklahoma , in the south-central part of the state .
Girl 's mother was found dead inside parked RV ; estranged husband sought for questioning . Police say man , girl presumed to be traveling in a white 1992 Toyota Paseo . Authorities think man has connections to Rockport , Texas , so Amber Alert issued there . Sheriff 's Office said girl has a medical condition that requires medication .