Affective interethnic ties are highly effective for improving out-group attitudes, especially during adolescence. Yet, young people face several obstacles to developing such ties in society. One potential means of fostering greater interethnic connectivity is through youth engagement: that is, formal, organized social participation in groups, clubs, or activities. However, little is still known about its effectiveness; especially for overcoming structural obstacles to contact in society, such as residential segregation. This study has two aims: to robustly examine whether youth engagement can build positive interethnic contact among young people; and, to perform the first systematic test of whether sites of engagement can act as "Associational Bridges", providing greater opportunities for contact among youth from more segregated environments. To pursue these aims, the study exploited a unique data opportunity to perform a quasi-experimental analysis of a large-scale, nationally-implemented youth engagement scheme in the United Kingdom. The study uses pre-test/post-test data on N = 1371 participants (M age = 16.7; 63% Female; 36% non-White) and N = 1946 propensity-score matched controls (M age = 16.7; 62% Female; 36% non-White). Applying a (matched) difference-indifference approach, the findings demonstrate that participation led to an increase in affective interethnic ties, which were evident at least 4-6 months after involvement had ended. Participation also had a stronger positive impact on youth from more residentially segregated areas: although joining the scheme with fewer interethnic ties, post-participation they reported just as many ties as their peers from less segregated areas. However, participation had no difference in effects for youth from more or less ethnically diverse areas. Youth engagement may thus be an effective tool for fostering positive contact; particularly among those from more segregated environments. However, attention should be paid to the design and recruitment practices of engagement programs to understand which structural barriers to contact in society they can overcome.