A small deviation.
One of the problems that Marvel writers run into is The Punisher. How do you make recurring characters for a guy whose whole schtick is that he kills off villains? Answer: Focus on his allies.
A Shadowrunning team often develops a nemsis, at least for an season's worth of episodes, like, say, "Mister Lanister, director of
Simtastic Studios, an entertainment firm under the Amalgamated Studios brand. Lanister's a ruthless bastard with his hands in several pies ... his starlets are addicted to BTLs, so he can mercilessly wring them out (And take advantage of them as a side bonus), he's in bed with teh Yaks, a street gang (The Actor's Guild, a gang who all wear bad halloween masks of famous actors) is in his pocket as his studio makes the BTLs that they distribute and he uses them to lay some weight on people, he's looking to buy up land near his studio to expand and doesn't care where the current occupants wind up, he's invested in several local businesses, he has a few fixers on call who, in addition to their normal work, also scout for acting talent (Movies with Shadowrunners in the lead always sell well!) ... he's just in a lot of places at once, with a light hand.
This lets his name keep popping up, his company pop up, but you can't get directly at him until you climb up the ranks a bit. Go through the "MidBosses" until you get to the Main Boss, as it were.

You should also focus on friends and allies, who *aren't* getting shot by teh runners, and expand their stories now and then, to remind them that things happen off camera.
A regular one is, of course, other Shadowrunning teams. Six is the number of choice as it's small enough to learn and large enough to factionalize (7 entities is the sociology standard for maximum Michavellianness and teh PCs count as one of those.) This gives job rivals who will be bidding for the same jobs as the PCs, who might show up in opposition to them at some point (Sorry chummers, it's just biz), who can be used as contacts or who can use the RUNNERS as contacts (Nothing more fun that having an NPC call up a PC and try to use them as a Legwork source, just to show them what it sounds like form the other side)... Give each group a name, a hook, and fill in members as needed. For example:
0) Baker's Dozen, a legender street team lead by one Charlie Baker and held up as the gold standard in the city for what a Shadowrunning team should be like. Depite the name, there are only five members. They eventually hit "The Big Time" and got hired by Ares a full-time assets. They live in high-rise apartments, eat real food, get a steady paycheck, have SINs... can you imagine it?
1) The Boomers. A group of runners who're known for outrageous behavior, loud noise, explosions, and no self restraint. They get monkeywrenching and distraction jobs almost exclusively as they wouldn't know subtle if it hit them with a brick to the face. Bright colors! Loud voices! CHAINSAW HANDS!!!
2) The Sisterhood. An all-female runner team that's more famous (rightly or wrongly) for being assembled from other runners based on looks. All of them have SimRecorders and sell their exploits via underground SimDealers. The tend to be flashy when on camera but can do it sneaky as well.
3) Warf Rats. From a poorer section of the city, they're known for doing anything if teh price is right ... wetwork, rape, burning down churches, whatever. As long as nuyen is involved, they don't care. Kinda craven, they dislike direct opposition or anyone who can fight back. They have a lot of friends in low places, and their leader is in tight with teh Rat Shaman guild (as he's a rat shaman) ... those who cross them wind up having ritual issues.
4) Johnny Five. Fairly new band that's still feeling their way around. Roughly 1 die less in all important skills than the PC Shadowrunning team. Every member's name is John in one way or another.
5) Knights of the Drop Tables. A Decker-heavy team that is good at sneaky infiltration but terribly in a stand-up fight. Tend to crow loudly about their victories, always hacking seme grafitti or reprogramming the I/C to say "Ni!" to every login, and so on. Good at what theyd o, but that evidence is going to come back and haunt them and everyone knows it.
6) Shadowrun Inc, a large team (Over a dozen members!) that has a rotating mission basis, where members are called in based on their talents as it applies to the mission. Very professional, but not terribly loyal to one another. Largely expected to be the next group to 'Sell out' and go Corporate (If they haven't already! Oh rumor mongers...)
7) The Green Machine, a band of 'hooding Shadowrunners with a clear social concious. Do lots of pro bono work and target polluting or anti-meta corps whenever possible. Quite adept at demolitions.
From there, add some other fixers (Some of which might want to hire the team away from their current fixer, up to and including having Shadowruns called against their current guy!), deckers, Samurai... give everyone at least one friend, a rival, and eventually an enemy. As you pad out NPCs, they'll start doing things and growing.
For instance, one I use is Shakey Sam, the Tremblin' Man. He's old (late 50's), has to shuffle instead of walk, has trouble speaking at times, and is well known for the shakes that always have him ... his hands are the worst. He looks to be homeless and is fairly unkempt and smells a bit, but there're many hushed rumors about him. Nobody ever looks at him as he's "Shamed" by his condition, but they all watch him out of the corner of their eyes. It's said that he was the very first Street Samurai, a living legend, but that his 'wires went bad over the years and now, well, this is what the future holds for young Samurai. You live too long, you don't go out in a blaze of glory, you wind up old, decrepit, and your body betrays you. You look at him too long, you realize that that could be you, and that's to hard for most people to accept. Shakey Sam goes around to assorted bars and eateries, but he won't take charity exactly. You can't buy him a drink or food, but you buy some of his art ... he paints, you see, and sells his (Bad, due to his hands) art, which he trades for food or drink.
Rumor is that two years back, one punk had too much to drink and started pushing Sam around. Made a big show of it like he was a big guy... until Sam slashed his face with a katana from seemingly nowhere at a speed no one could follow. Perfectly smooth, not a hint of tremble, absolutely perfect swing that gave the punk a "wide smile"as the blade went through each side of his mouth, never hitting a tooth. He managed a bow, sheethed the sword, then left quietly. (Tracking this rumor down? It's true! A waitress who was there can also add that, after he got outside, Sam had an absolute fit, his body shaking worse than ever as part of his nervous system decayed from the activity. She helped him for a couple of days and found out way more, but keeps it private)
Sam could serve as a mentor for the team's Samurai, teaching him all manner of customs that he learned back when he was a Renraku man. He paints, does calligraphy, archery, is an absolute master of the blade, but his greatest love is a proper tea ceremony. Undertaking it in his condition is insanely hard, of course, but he'd love nothing more to find a right, honorable person to pass his knowledge to before he dies.
Maybe the group will ignore him, maybe they'll worry about him, but he'll be there as an NPC, full of backstory, whenever needed.
Don't be discouraged if people don't play with your toys, however. Sometimes, people don't care about that Ork with five kids to feed and a lucky rabbit's foot ... they just want to shoot a Tuskr and call it a day.