Today’s first glitch:
Change the comma after viaduct to a period and capitalize Searchlights (notice the plural to go with the linking verb are). In the last sentence, the antecedent for the pronoun they is unclear; change it to a noun or rewrite the sentence. The preposition beyond doesn’t quite work with curfew and would be better replaced with past.
A couple of teenagers are crouched down, hidden in the shadows of a grimy viaduct. Searchlights are sweeping the streets. The teenagers are out past curfew.
I think this would work better if rewritten slightly, although it’s more a matter of personal taste than anything else.
A couple of teenagers are crouched down and hidden in the shadows of a grimy viaduct while searchlights sweep the streets. They’re out past curfew.