Couldn't it also be in command form?
You could only give commands like this in second person. So it would be either "Nu mă urmări!" (singular) or "Nu mă urmăriți!" (plural/polite).
Is this only in Romania? At least in Moldova, informal commands are formed using the third person.
For the singular imperative, if it's positive it should be third person singular. If it's negative then it should be 'nu' +infinitive.
The exclamation mark is used for vocativ case, so this sentence must be only for second person, like potestasity said: "Nu mă urmări!", at singular, or "Nu mă urmăriți!", at plural. "Nu mă urmărește!" is a mistake, a nonsense.
Correct: This is not Vocativ case. It is Imperative mode