In regards to this language peeve, the difference between "went missing" and "is missing" is a bit more involved than one might initially think...not only are the verbs in the phrases different, the verb type and tense are different as well. These verbal differences result in semantic differences, and the choice of using one phrase rather than the other may or may not be intentional.
Went is the past tense form of the verb to go. To go is an action verb.
Is is a present tense form of the verb to be. To be is a verb of being that is considered a linking verb.
Semantically, action verbs imply that choice is involved because people choose their actions, whereas linking verbs simply form an association between a subject and its complement. So, saying that a person "went missing" implies that that person chose to go missing and saying a person "is missing" implies that there was not a choice and that whatever happened was against that person's will. Additionally, because went is past tense, "went missing" leaves open the possibility that the person is no longer missing.
The choice of using one phrase rather than the other may be intentional if the possibility exists that the missing person is on the lam or it could just be that a copywriter was lazy and didn't give much thought to the semantics of the chosen verb.