Just ride. You'll find folk.
I hear there is a casual group meet up at the Jax Bike Center on Saturdays around 8am. (or something like that)
Although riders are out far earlier.
-------Cal Spas--- they ride fast... they start where "IE Bikes" "used to be" on Whitewood. That's about all I know. Pedal Mashing all the way, 25-30mph, you may be dropped.
-------Ride up and down Whitewood/Margarita From the 79 to Menifee. Most days you'll see folk there.
-------Or ride south on Clinton Keith up onto the Santa Rosa Mesa... you can do an out and back turning around on Los Gatos, BUT DO NOT GO DOWN LOS GATOS. It is POSSIBLE to go down and do a loop around to De Luz (I think) and come down into Temecula from Rainbow, but once you commit to going down, heading back is NEAR IMPOSSIBLE without mountain bike gearing and an iron lung. If you go down, don't let off your brakes, ever. If you let go for 4sec. you'll quickly accelerate over 50mph, and melt your brakes trying to slow down. (Los Gatos is between 13%-30% grade...) I once heard of a person who was new to the Cal Spas riding group who "bombed" down the road, he didn't stop until he hit a solid wall across the intersection at the bottom. He left in an ambulance and the police report said he hit the wall "over 70mph".
-------You'll also see bikes heading out toward's Tom's Farms (and back) on Temescal Canyon
-------Or take Temescal Canyon to Green River and down the Santa Ana River Trail to Huntington Beach. (if you go one way it is 60 miles from Elsinore, 75 from Temecula) (plan someone to pick you up or ride back.
-------From the 79 you can ride over to Rainbow
-------Or take the 79 out to the Temecula Wine Country, you'll often see bikes on the side roads wandering the rollers between vineyards.