Results are reported from a search for the top squark t 1 , the lighter of the two supersymmetric partners of the top quark.The data sample corresponds to 19.7 fb -1 of proton-proton collisions at √ s = 8 TeV collected with the CMS detector at the LHC.The search targets t 1 → b χ ± 1 and t 1 → t ( * ) χ 0 1 decay modes, where χ ± 1 and χ 0 1 are the lightest chargino and neutralino, respectively.The reconstructed final state consists of jets, b jets, missing transverse energy, and either one or two leptons.Leading backgrounds are determined from data.No significant excess in data is observed above the expectation from standard model processes.The results exclude a region of the two-dimensional plane of possible t 1 and χ 0 1 masses.The highest excluded t 1 and χ 0 1 masses are about 700 GeV and 250 GeV, respectively.