New technologies are changing people’s lifestyles and in turn, their way of relating to and interacting with others. Breadcrumbing is one of the new 2.0 concepts linked to the virtual relationship paradigm. This study aimed to design and psychometrically test the Breadcrumbing in Affective-Sexual Relationships (BREAD-ASR) Questionnaire to explore breadcrumbing perpetration in adolescent relationships online. A total of 247 adolescents participated in a paper-and-pencil survey carried out from March to June 2019 in a high school in southeastern Spain. Psychometric analysis showed a satisfactory content and construct validity for the instrument. The ordinal alpha coefficient was 0.83, indicating the BREAD-ASR questionnaire had good internal consistency. The BREAD-ASR questionnaire constitutes a valid and reliable instrument which can be used by health professionals in screenings for breadcrumbing perpetration and to design effective prevention and intervention programs in the community, which may help and support adolescents and families to deal with new forms of online relationships and perpetration successfully.