Abstract Background Internet addiction (IA) has been consistently associated with adverse mental health outcomes, but less is known about whether adolescents with IA seek mental health support, and whether associations between help-seeking and mental health problems differ across pathways. Objective This study aimed to describe mental health help-seeking patterns across internet use and IA status, and examine the independent and interactive associations of IA and help-seeking with mental health problems. Methods Data were drawn from 2 repeated cross-sectional surveys conducted in Shandong Province in 2023 and 2024. A total of 171,970 junior middle school students were included. IA was assessed using a 9-item scale adapted from DSM-5 ( Diagnostic and Statistical Manual of Mental Disorders [Fifth Edition]) Internet Gaming Disorder criteria to assess internet use–related symptoms. Students using the internet for at least 4 hours per day and endorsing at least 4 symptoms were classified as having IA. Help-seeking was categorized as no help-seeking, informal-only help-seeking, and any formal help-seeking. Mental health problems were defined as clinically significant depressive or anxiety symptoms. Pairwise logistic regression compared help-seeking patterns, and Poisson regression with school-clustered CR2 robust SEs estimated adjusted prevalence ratios (PRs). Results Overall, 1.4% (2406/171,970) met the definition of IA; 47.9% (82,402/171,970), 42.1% (72,461/171,970), and 9.9% (17,107/171,970) reported no help-seeking, informal-only help-seeking, and any formal help-seeking, respectively. Among adolescents with IA, 59.9% (1440/2406) reported no help-seeking, 33.8% (814/2406) reported informal-only help-seeking, and only 6.3% (152/2406) reported any formal help-seeking. Compared with nonaddictive internet users, adolescents with IA had lower odds of informal-only versus no help-seeking (OR [odds ratio] 0.690, 95% CI 0.631‐0.754), any formal versus no help-seeking (OR 0.540, 95% CI 0.455‐0.640), and any formal versus informal-only help-seeking (OR 0.786, 95% CI 0.659‐0.937). Compared with nonaddictive internet users, adolescents with IA had a higher prevalence of mental health problems (PR 3.662, 95% CI 3.428‐3.912). Informal-only (PR 0.581, 95% CI 0.550‐0.614) and any formal help-seeking (PR 0.461, 95% CI 0.420‐0.505) were associated with lower prevalence overall. Interaction terms for IA with informal-only help-seeking (PR 1.469, 95% CI 1.336‐1.616) and any formal help-seeking (PR 2.033, 95% CI 1.696‐2.437) indicated weaker inverse associations among adolescents with IA. Within the IA group, informal-only help-seeking was associated with lower prevalence (PR 0.848, 95% CI 0.784‐0.917), whereas any formal help-seeking was not clearly associated with lower prevalence (PR 0.945, 95% CI 0.814‐1.097). Sensitivity analyses supported these patterns. Conclusions Adolescents with IA had a substantially higher prevalence of clinically significant depressive and anxiety symptoms and were less likely to report mental health help-seeking, especially formal help-seeking. These findings highlight a high-burden, low help-seeking subgroup and suggest strengthening school-based mental health services, improving linkage between informal and formal support, reducing stigma, and developing low-threshold digital mental health pathways.