Active　friending　is　a　problem　in　social　networks　that　is　to　assist　a　user　to　build　a　relationship　to　a　target　user　by　sending　invitations　to　a　set　of　intermediate　users;　the　goal　is　to　maximize　the　acceptance　probability　at　the　target　node　taking　advantage　of　the　social　influence　through　the　network　formed　by　the　intermediate　nodes.　In　this　paper,　we　convert　the　original　formulated　active　friending　problem　of　nonsubmodular　maximization　subject　to　cardinality　constraint　into　a　submodular　cost　submodular　knapsack　problem　in　the　IC　model,　and　we　show　that　the　two　problems　are　equivalent.　We　similarly　make　the　conversion　on　the　active　friending　in　the　LT　model.　Then　we　give　a　general　combinatorial　optimization　algorithm　to　solve　active　friending　problems　in　both　the　IC　model　and　the　LT　model　with　a　guaranteed　approximation.　We　analyze　the　computational　complexity　of　the　problem　and　the　algorithm　performance.　The　effectiveness　of　the　generalized　method　is　verified　on　real　data　sets.　©　2020,　Springer-Verlag　GmbH　Austria,　part　of　Springer　Nature.