Do you have an existing CRM that you use to track donations? If so, you may want to look into peer-to-peer fundraising platforms that connect directly with your CRM. Team Raiser is a good, robust choice. Friend Raiser (I think that's what it's called) is also good, but these have a bigger upfront cost. Both systems will connect to salesforce, and Friend Raiser is a Blackbaud product. Salsa Labs also has a peer-to-peer solution, but I'm not familiar with it.
If you want something with no upfront cost, then I recommend crowdrise, which just charges per transaction, but there will be crowdrise branding everywhere rather than just your brand. They may have a white label option for additional $$.