I want to invest a small amount of money 5-10K into one or several startups in exchange for the share in the company. I would be also interested to contribute to the startups I invested into with my experience or connections/contacts if it's applicable.

Are there any services/companies that allow me to do this at this moment?

Note: this service should be available for regular people with relatively small amount of money but not for big investors and venture capital companies.

If it such a thing doesn't exist now... what problems would I face if I decide to build it myself?

Thank you