触る was originally just an intransitive verb, but in recent years it's also being used as a transitive verb (probably because it's so close in meaning to 触れる).
Sometimes it's difficult to tell whether it's being used as a transitive/intransitive verb when the object and particle are omitted, but either way there's not much of a difference in meaning, so I wouldn't worry about it. Here are a few examples:
触る (intransitive):
肩に触る - to touch [someone] on the shoulder
展示品には触らないでください。 - Please do not touch the exhibit.
触る (transitive):
壁を触る - to touch a wall
子どもたちがウサギを触ってはしゃぎ回る。 - The children are happily petting the rabbits and frolicking about.