The process of nanowhisker formation on the substrates activated by catalyst drops was investigated by Monte Carlo simulation. Influence of deposition conditions on whisker morphology was considered. Straight whiskers with uniform diameter could be grown using catalyst possessing large contact angle with whisker material. It was demonstrated that variation of growth conditions in such physicochemical system may result in nanotube formation. Atomic mechanism of hollow whisker formation was suggested. The range of model growth conditions for nanowhisker and nanotube formation were identified.