This Is Zimbabwe has several suggestions for action you can take regarding the abductees. The one I have picked on is the AVAAZ Speak Out For Zimbabwe campaign.
It is certainly better to get involved with this than do nothing.
It is unlikely that Motlanthe will listen to any petitions There is a deeper problem with the intractable Zimbabwe problem. I used to argue with people who, in the days of Thabo Mbeki's problems with Zuma at Polokwane, spoke with such authority about how Zuma would read the riot Act to Mugabe and tell him where to get off. They "reasoned" that because Zuma had the support of COSATU, he would be pressured into action by that body.
Well, I have met some of these people after Zuma's ascendancy. Typically, their response now was what it was when Mbeki was in power: "All these African leaders are the same. Zuma is afraid of COPE challenge so does not want an opposition to succeed in Zimbabwe.."
People, please! I think we are running out of people to run to with our problems, don't you agree?