When an officer stops a juvenile while walking, what are their obligations as a citizen?

Whose obligations, the juvenile? Well if the juvenile feels he or she is being detained (no reasonable method of leaving) and feel he or she is being interrogated, I believe a parent must be there. 

If out on the street, depends on what happens -- is the officer conducting a pat down of the juvenile based on a reasonable articulable suspicion he or she is carrying contraband?

Here are some relevant laws for your review:  NRS 171.123  Temporary detention by peace officer of person suspected of criminal behavior or of violating conditions of parole or probation: Limitations.

      1.  Any peace officer may detain any person whom the officer encounters under circumstances which reasonably indicate that the person has committed, is committing or is about to commit a crime.

      2.  Any peace officer may detain any person the officer encounters under circumstances which reasonably indicate that the person has violated or is violating the conditions of his parole or probation.

      3.  The officer may detain the person pursuant to this section only to ascertain his identity and the suspicious circumstances surrounding his presence abroad. Any person so detained shall identify himself, but may not be compelled to answer any other inquiry of any peace officer.

      4.  A person must not be detained longer than is reasonably necessary to effect the purposes of this section, and in no event longer than 60 minutes. The detention must not extend beyond the place or the immediate vicinity of the place where the detention was first effected, unless the person is arrested.

      (Added to NRS by 1969, 535; A 1973, 597; 1975, 1200; 1987, 1172; 1995, 2068)

      NRS 171.1231  Arrest if probable cause appears.  At any time after the onset of the detention pursuant to NRS 171.123, the person so detained shall be arrested if probable cause for an arrest appears. If, after inquiry into the circumstances which prompted the detention, no probable cause for arrest appears, such person shall be released.

      (Added to NRS by 1969, 535)

      NRS 171.1232  Search to ascertain presence of dangerous weapon; seizure of weapon or evidence.

      1.  If any peace officer reasonably believes that any person whom he has detained or is about to detain pursuant to NRS 171.123 is armed with a dangerous weapon and is a threat to the safety of the peace officer or another, the peace officer may search such person to the extent reasonably necessary to ascertain the presence of such weapon. If the search discloses a weapon or any evidence of a crime, such weapon or evidence may be seized.

      2.  Nothing seized by a peace officer in any such search is admissible in any proceeding unless the search which disclosed the existence of such evidence is authorized by and conducted in compliance with this section.

      (Added to NRS by 1969, 535)