Tone injection (TI) is an effective technique to overcome high PAPR (peak-to-average power ratio) of OFDM. The PAPR reduction problem solved with TI is a combinatorial problem. Although the effectiveness of GA has been demonstrated for this problem, GA involves relative complex operators. This implies that, when implementing the methods of TI on digital circuits, other methods may outperform GA under the same processing time. In this paper, we investigate effective parallel search methods for the PAPR reduction, which are of simple structure for implementing digital circuits. At first, as the basis of the parallel methods, we propose two types of stochastic search methods. The one is Flip-Probability-specified type (FP) search and the other is a specified-Number-of-Flips type (NF) search. Both of them use only simple stochastic operators. Then, we propose an effective digital circuit implementation of the solution evaluation function. Finally, we propose a parallel search method based on FP and NF search. The simulation results show that, the proposed parallel search methods can improve not only the processing speed but also the quality of the solution.