Startups get approached all the time (ones with traction & articles written about them) so simply tell the founder you love the company and would like to invest

Startups get approached all the time (ones with traction & articles written about them) so simply tell the founder you love the company and would like to invest. If he has raised money he will not be turned off by your approach. Your best bet is to join in a round (if it is open) otherwise, it may not be feasible given the other investors and legal issues involved.