This work reports on magnetic measurements of the quasi-two-dimensional (quasi-2D) system Zn1-xMnxIn2Se4, with 0.01≤x≤1.00. For x>0.67, the quasi-2D system seems to develop a spin-glass behaviour. Evidence of a true phase transition phenomenon is provided by the steep increase of the nonlinear susceptibility χnl when approaching TC from above. The static scaling of χnl data yields critical exponents δ = 4.0 0.2, = 4.37 0.17 and TC = 3.4 0.1K for the sample with x = 1.00 and similar values for the sample with x = 0.87. These critical exponents are in good agreement with values reported for other spin-glass systems with short-range interactions. © 2008 IOP Publishing Ltd.