We present searches for massive top and bottom quark partners at CMS using LHC pp collision data collected at centre-of-mass energy $sqrt{s} = 8$ TeV. Such partners can be found in models predicting vector-like quarks to solve the hierarchy problem a
nd stabilize the Higgs boson mass. The searches span a range of final states containing several lepton and jet multiplicities, and limits were set on mass and production cross sections as a function of branching ratios.
