The aim of this meta-analysis was to summarize the most recent data about the association between Problematic Social Networking sites use (PSNSU) and depression and anxiety. Moreover, to further extent the literature, we examined the relationship between PSNSU and stress. PubMed/Medline and Scopus were searched from March 2016 to January 2022 to retrieve studies that evaluated the relationship between SNSs addiction and depression, anxiety, and stress. Moderator analyses (meta-regression and subgroup analyses for continuous and categorical variables, respectively) were used to examine variability across studies. Thirty-eight studies (pooled N=29,944; 63.1% females, Mage 21.8, range: 10.4–50.1 years) were eligible. Results of random effects meta-analysis confirmed a positive correlation between SNSs addiction and depression (r = 0.30, 95%CI [0.26–0.33]), stress (r = 0.29, 95%CI [0.21–0.36]), and anxiety (r = 0.30, 95%CI [0.26–0.34]; corrected correlation for publication bias r = 0.22, 95%CI [0.17–0.27]). Subgroup analysis revealed that the aforementioned correlations were significantly larger for Western countries (Europe and North America) than Asian countries. For the relationship between SNS addiction and depression, meta-regression analysis showed that the correlation was weaker for samples with a higher percentage of females (k = 30) (β = −0.32, p = 0.006), accounting for 25.77% of the heterogeneity. Regarding the effect sizes resulting by the present study, they can be considered as weak to moderate. Future studies should focus on longitudinal designs to establish directionality between PSNSU and psychiatric symptoms, as well as prevention strategies and randomized controlled interventions with respect to demographic and cultural factors.